JP2022033831A - Graphene oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide graphene oxide with sufficient dispersibility in a solvent, where graphene obtained by reducing the graphene oxide has high electrical conductivity.

SOLUTION: This invention provides graphene oxide in which a ratio (C/O) between carbon atoms and oxygen atoms in X-ray photoelectron spectroscopic analysis is from 2.5 to 4 inclusive. The graphene oxide has moderate dispersibility in a solvent, and graphene obtained by reducing the graphene oxide has high electrical conductivity and is suitable as an auxiliary conductive agent used for an active material layer of a secondary battery.

SELECTED DRAWING: None

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to graphene oxide. It should be noted that one aspect of the present invention is not limited to the above technical fields. The technical field of one aspect of the invention disclosed in the present specification and the like relates to a product, a method, or a manufacturing method. Alternatively, one aspect of the invention relates to a process, machine, manufacture, or composition (composition of matter). Therefore, more specifically, the technical fields of one aspect of the present invention disclosed in the present specification include semiconductor devices, display devices, liquid crystal displays, light emitting devices, lighting devices, power storage devices, storage devices, and driving methods thereof. Alternatively, those manufacturing methods can be given as an example.

With the remarkable spread of portable electronic devices such as mobile phones, smartphones, electronic books (electronic books), and portable game machines in recent years, there is an increasing demand for smaller and larger capacity secondary batteries, which are the driving power sources for them. There is. As a secondary battery used in a portable electronic device, a secondary battery typified by a lithium secondary battery having advantages such as high energy density and large capacity is widely used.

Among secondary batteries, lithium secondary batteries, which are widely used due to their high energy density, are positive electrodes containing active materials such as lithium cobalt oxide (LiCoO ₂ ) and lithium iron oxide (LiFePO ₄ ), and lithium ions. A negative electrode made of a carbon material such as graphite that can be stored and released, and an organic solvent such as ethylene carbonate or diethyl carbonate, LiBF ₄ or Li
It is composed of a non-aqueous electrolyte solution in which an electrolyte composed of a lithium salt such as PF ₆ is dissolved. Charging and discharging of the lithium secondary battery is performed by the lithium ions in the secondary battery moving between the positive electrode and the negative electrode via the non-aqueous electrolytic solution, and the lithium ions are inserted into and desorbed from the active material of the positive electrode and the negative electrode.

A binder (also referred to as a binder) is mixed in the positive electrode or the negative electrode in order to bind the active material to the active material or the active material to the current collector. The binder is an insulating PVdF (polyvinylidene fluoride).
Since high molecular weight organic compounds such as these are common, their electrical conductivity is extremely low. Therefore, if the ratio of the amount of the binder mixed in to the amount of the active material is increased, the amount of the active material in the electrode is relatively reduced, and as a result, the discharge capacity of the secondary battery is reduced.

Therefore, by mixing a conductive auxiliary agent such as acetylene black (AB) or graphite particles, the electrical conductivity between the active materials or between the active material and the current collector is improved. This makes it possible to provide a positive electrode active material having high electrical conductivity (see Patent Document 1). There are also reports of using graphene as a conductive aid.

Japanese Unexamined Patent Publication No. 2002-110162

One of the purposes of the present invention is to provide graphene oxide having sufficient dispersibility in a solvent and having high electrical conductivity of graphene obtained by reducing the graphene oxide. Alternatively, one of the purposes is to provide graphene oxide having sufficient dispersibility in a solvent. Another object of the present invention is to provide graphene oxide having high electron conductivity of graphene obtained by reducing graphene oxide. Alternatively, one of the purposes is to provide a novel graphene oxide. or,
One of the purposes is to provide new materials. Alternatively, one of the purposes is to provide a new power storage device. The description of these issues does not preclude the existence of other issues.
It should be noted that one aspect of the present invention does not necessarily have to solve all of these problems. note that,
Issues other than these are self-evident from the description of the description, drawings, claims, etc., and it is possible to extract problems other than these from the description of the specification, drawings, claims, etc. ..

One aspect of the present invention is that the ratio (C / O) of carbon atom to oxygen atom in X-ray photoelectron spectroscopy is 2.
Graphene oxide of 5 or more and 4 or less.

Another aspect of the present invention is graphene oxide having a carbon atom to oxygen atom ratio (C / O) of 3 or more and 4 or less in the above configuration.

Another aspect of the present invention is graphene oxide having a carbon atom to oxygen atom ratio (C / O) of 3 or more and 3.7 or less in the above configuration.

The figure explaining the positive electrode. The figure explaining the coin-shaped secondary battery. The figure explaining the electrophoresis method and the electrochemical reduction method. The figure explaining the laminated type secondary battery. The figure explaining the cylindrical secondary battery. Diagram illustrating a thin secondary battery The figure explaining the thin secondary battery. The figure explaining the radius of curvature of a surface. The figure explaining the radius of curvature of a film. The figure for demonstrating the example of a power storage device. The figure for demonstrating the example of a power storage device. The figure for demonstrating the example of a power storage device. The figure for demonstrating the example of a power storage device. The figure for demonstrating the example of an electric device. The figure explaining the electronic device. The figure explaining the electronic device. The figure explaining the electronic device. The figure explaining an example of an electronic device. The relationship between the amount of oxidant consumed per weight of substrate graphite and the reaction time. FT-IR measurement result. The discharge curve of the secondary battery produced in Example 1.

Hereinafter, embodiments will be described with reference to the drawings. However, it is easily understood by those skilled in the art that embodiments can be implemented in many different embodiments and that the embodiments and details can be varied in various ways without departing from the spirit and scope thereof. .. Therefore, the present invention is not construed as being limited to the description of the following embodiments.

In each of the figures described herein, the size, film thickness or region of each configuration may be exaggerated for clarity. Therefore, it is not necessarily limited to that scale.

(Embodiment 1)
In this embodiment, the outline of graphene oxide according to one aspect of the present invention will be described. Graphene is a carbon material having a crystalline structure in which a hexagonal skeleton formed by carbon is extended in a plane. Graphene is an atomic surface of a graphite crystal, and has amazing characteristics in electrical, mechanical, or chemical properties. Therefore, graphene is used for high mobility field effect transistors and high sensitivity. It is expected to be applied in various fields such as sensors, highly efficient solar cells, and transparent conductive films for the next generation, and is attracting attention.

As used herein, graphene includes single-layer graphene or multi-layer graphene having two or more layers and 100 or less layers. Single-layer graphene refers to a sheet of carbon molecules in a monoatomic layer having a π bond. Further, graphene oxide refers to a compound in which the graphene is oxidized. When graphene oxide is reduced to form graphene, all oxygen contained in graphene oxide may not be desorbed, and some oxygen may remain in graphene.

Here, when the graphene is a multilayer graphene, the graphene is a graphene obtained by reducing graphene oxide (hereinafter referred to as RGO (hereinafter referred to as RGO as an abbreviation for Redicated Graphene Oxide)), and the interlayer distance of graphene is 0.34 nm or more and 0.5 nm or less. It is preferably 0.38 nm or more and 0.42 nm or less, and more preferably 0.39 nm or more and 0.41 n.
It is less than m. In ordinary graphite, the interlayer distance of single-layer graphene is 0.34 nm, and the graphene used in the secondary battery according to one aspect of the present invention has a longer interlayer distance.
It facilitates the transfer of carrier ions between layers of multilayer graphene.

In the positive electrode for a secondary battery using graphene as a conductive auxiliary agent, graphene is dispersed in the positive electrode active material layer so as to be in contact with a plurality of positive electrode active material particles. In other words, it can be said that a network for electrical conduction by graphene is formed in the positive electrode active material layer. As a result, the bonding of the plurality of positive electrode active material particles is maintained, and as a result, a positive electrode active material layer having high electrical conductivity can be formed.

The positive electrode active material layer to which graphene is added as a conductive auxiliary agent can be produced by the following method. First, a dispersion medium (also referred to as a solvent) is added to graphene and the positive electrode active material, and the mixture is kneaded to prepare a mixture. A binder (also referred to as a binder) is added to this mixture and kneaded to prepare a positive electrode slurry. Finally, after applying the positive electrode slurry to the positive electrode current collector, the dispersion medium is volatilized, and graphene is added as a conductive auxiliary agent to prepare a positive electrode active material layer.

However, in order to use graphene as a conductive additive to form a network of electrical conduction in the positive electrode active material layer, graphene must first be uniformly dispersed in the dispersion medium. This is because the dispersibility in the dispersion medium depends directly on the dispersibility of graphene in the positive electrode active material layer, and when the dispersibility of graphene is low, the graphene aggregates and localizes in the positive electrode active material layer. This does not lead to the formation of the network. Therefore, it can be said that the dispersibility of graphene used as a conductive additive in a dispersion medium is an extremely important factor for enhancing the electrical conductivity of the positive electrode active material layer.

However, the positive electrode active material layer prepared by putting graphene as a conductive auxiliary agent in a dispersion medium together with an active material and a binder does not have sufficient dispersibility of graphene, and as a result, for electrical conduction in the positive electrode active material layer. It is difficult to form a network. Furthermore, instead of graphene as a conductive auxiliary agent, R
The same applies to the positive electrode active material layer prepared by putting GO in a dispersion medium because the dispersibility of RGO is not sufficient.

On the other hand, graphene oxide (GO (abbreviated as GO for Graphene Oxide) is referred to as GO) is put into a dispersion medium together with an active material and a binder to prepare a positive electrode paste, and then the dispersed graphene oxide is reduced by heat treatment. In the positive electrode active material layer as RGO, a network of electric conduction is formed in the active material layer, and excellent electric conductivity is exhibited.

These facts are that the dispersibility is low in the positive electrode active material layer in which graphene or RGO is dispersed as a raw material of the conductive auxiliary agent, whereas the dispersibility of graphene reduced after adding graphene oxide to form a positive electrode paste is high. Is shown.

From the above, in order to use graphene as a conductive auxiliary agent and to construct a network having high electrical conductivity in the positive electrode active material layer, graphene oxide having high dispersibility is used as a dispersion medium at the time of preparing the positive electrode paste. It is effective to use. The dispersibility of graphene oxide in the dispersion medium is considered to depend on the amount of oxygen-bearing functional groups such as epoxy groups (expressed as the degree of oxidation).

Here, graphene oxide is synthesized by oxidizing graphite, and the degree of oxidation of graphene oxide can be adjusted by the amount of the oxidizing agent used at that time. Graphene oxide, which has a high degree of oxidation, has excellent dispersibility and is suitable as a raw material for RGO used as a conductive auxiliary agent for active substances. However, the present inventors have found that RGO made from graphene oxide whose degree of oxidation is reduced to the extent that dispersibility is not impaired has good conductivity and is a useful material.

Therefore, one aspect of the present invention is graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less.

Here, the weight ratio of oxygen to carbon is an index showing the degree of oxidation, and the weights of carbon and oxygen among the constituent elements of graphene oxide are viewed as a ratio with respect to carbon. note that,
The weight of the elements constituting graphene oxide is, for example, X-ray photoelectron spectroscopy (XPS: X-ray).
It can be measured by Photoemission Spectroscopy).

Graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less is in a state in which functional groups such as an epoxy group, a carbonyl group, a carboxyl group and a hydroxyl group are bonded to such an extent that they have sufficient dispersibility for forming an electrode. Means that From the viewpoint of dispersibility, the weight ratio of oxygen to carbon is preferably 3 or more, and from the viewpoint of the conductivity of RGO, the weight ratio of oxygen to carbon is preferably 3.7 or less. That is, graphene oxide having a weight ratio of oxygen to carbon of 3 or more and 3.7 or less is more preferable in consideration of both dispersibility and conductivity in the case of RGO.

Therefore, graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less is dispersed in a dispersion medium together with a positive electrode active material and a binder, kneaded, coated on a positive electrode current collector, and heated. This makes it possible to form an electrode containing graphene, which is highly dispersible and has a network of electrical conduction.

The graphene oxide preferably has a side length of 50 nm or more and 100 μm or less, preferably 800 nm or more and 20 μm or less.

As described above, since the graphene oxide has a functional group sufficiently containing oxygen from the viewpoint of producing an electrode, the graphene oxide aggregates with each other in a polar solvent such as 1-methyl-2-pyrrolidone (NMP). Disperse evenly without doing. The dispersed graphene oxide is uniformly mixed with a plurality of granular positive electrode active materials. Therefore, by the volatilization of the dispersion medium and the reduction treatment of the graphene oxide, the graphene formed from the graphene oxide is dispersed in the positive electrode active material layer to the extent that it comes into surface contact with other graphene. Since graphene is in the form of a sheet and is electrically connected to each other by partial surface contact, it is considered that a network of electrical conduction is formed when each graphene is regarded as one set. Moreover, since the graphenes are connected to each other by surface contact, the contact resistance can be suppressed to a low level, and a network with high electrical conductivity can be constructed.

On the other hand, each graphene has a side length of 50 nm or more and 100 μm or less, preferably 8
Since the sheet is 00 nm or more and 20 μm or less and is larger than the average particle size of the granular positive electrode active material, one sheet-shaped graphene can be connected to a plurality of granular positive electrode active materials. In particular, since graphene is in the form of a sheet, it can be surface-contacted so as to cover the surface of the granular positive electrode active material. Therefore, the contact resistance between the granular positive electrode active material and graphene can be reduced without increasing the amount of the conductive auxiliary agent.

As the granular positive electrode active material, a material capable of inserting and removing carrier ions such as lithium iron phosphate can be used.

Subsequently, a method for manufacturing an electrode using the graphene oxide will be described. First, graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less and a positive electrode active material are dispersed in a dispersion medium.
Knead. A positive electrode slurry is prepared by adding a binder to this mixture and kneading, and the positive electrode slurry is applied to the positive electrode current collector. After or at the same time as volatilizing the dispersion medium contained in the applied positive electrode slurry, graphene oxide is reduced to form a positive electrode active material layer containing graphene (RGO) on the positive electrode current collector to form an electrode. Can be manufactured.

In the above production method, the positive electrode paste is dried in a reducing atmosphere or under reduced pressure. This makes it possible to volatilize the dispersion medium contained in the positive electrode paste and reduce graphene oxide contained in the positive electrode paste.

Further, in the above-mentioned production method, when the binder is added to the mixture and kneaded, the viscosity of the positive electrode paste can be adjusted by further adding a dispersion medium.

The positive electrode active material is added to a dispersion medium in which graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less is dispersed. By kneading this, a positive electrode active material layer with high dispersibility of graphene is formed. Graphene oxide may be contained in a proportion of at least 2 wt% (weight percent) with respect to the total weight of the positive electrode paste which is a mixture of the positive electrode active material, the conductive auxiliary agent and the binder. On the other hand, graphene after the positive electrode paste is applied to the current collector and reduced may be contained in a ratio of at least 1 wt% with respect to the total weight of the positive electrode active material layer. This is because the reduction of graphene oxide almost halves the weight of graphene.

Specifically, at the stage of the positive electrode paste, 2 graphene oxide is added to the total amount of the positive electrode paste.
Add wt% or more and 10 wt% or less, and add positive electrode active material of 85 wt% or more and 93 wt% or less.
It is preferable to add the binder in an amount of 1 wt% or more and 5 wt% or less. Further, at the stage of the positive electrode active material layer in which the positive electrode paste is applied to the current collector to reduce graphene oxide, graphene is added in an amount of 1 wt% or more and 5 wt% or less with respect to the total amount of the positive electrode active material layer, and the positive electrode active material is added. 90 wt% or more 9
It is preferable to add 4 wt% or less and add 1 wt% or more and 5 wt% or less of the binder.

After applying the positive electrode paste to the positive electrode current collector, it is dried in a reducing atmosphere or under reduced pressure to desorb oxygen contained in graphene oxide, whereby a positive electrode active material layer containing graphene can be formed. It should be noted that all the oxygen contained in graphene oxide is not desorbed, and some oxygen may remain in graphene.

By using the positive electrode, the negative electrode, the electrolytic solution, and the separator manufactured as described above,
A secondary battery can be manufactured. It should be noted that one aspect of the present invention can be applied to various power storage devices. For example, as an example of a power storage device, a battery, a primary battery, a secondary battery,
Examples include lithium-ion secondary batteries and lithium-air batteries. Further, as another example of the power storage device, it can be applied to a capacitor. In addition, graphene oxide can be used as an electrode for a supercapacitor, which is a capacitor with a very large capacity, as an oxygen reduction electrode catalyst, as a material for dispersed water with lower friction than lubricating oil, a display device, and the sun. A high-sensitivity nanosensor for detecting uranium and plutonium contained in radioactively contaminated water, as a transparent electrode for batteries, as a gas barrier material, as a lightweight polymer material with high mechanical strength, etc. It can be used as a material or as a material for removing radioactive substances.

(Embodiment 2)
In the present embodiment, an electrode for a secondary battery manufactured by using graphene oxide according to one aspect of the present invention will be described with reference to FIG. FIG. 1 shows a perspective view of the electrodes.

FIG. 1 is a perspective view of the positive electrode 200. Although the positive electrode 200 is shown in a rectangular sheet shape in FIG. 1, the shape of the positive electrode 200 is not limited to this, and any shape can be appropriately selected. The positive electrode 200 is produced by applying the positive electrode paste on the positive electrode current collector 201 and then drying it in a reducing atmosphere or under reduced pressure to form the positive electrode active material layer 202. In FIG. 1, the positive electrode active material layer 202 is formed only on one surface of the positive electrode current collector 201, but the positive electrode active material layer 202 may be formed on both surfaces of the positive electrode current collector 201. Further, the positive electrode active material layer 202 does not need to be formed on the entire surface of the positive electrode current collector 201, and a non-coated region such as a region for connecting to the positive electrode tab is appropriately provided.

The positive electrode current collector 201 is not particularly limited as long as it exhibits high conductivity without causing a remarkable chemical change in the power storage device. For example, metals such as aluminum, stainless steel, gold, platinum, zinc, iron, nickel, copper, titanium, tantalum and manganese, alloys thereof, sintered carbon and the like can be used. Further, copper or stainless steel may be coated with carbon, nickel, titanium or the like. Further, an aluminum alloy to which an element for improving heat resistance such as silicon, neodymium, scandium, and molybdenum is added can be used. Further, it may be formed of a metal element that reacts with silicon to form silicide. Metallic elements that react with silicon to form silicides include zirconium, titanium, hafnium, vanadium, niobium, and so on.
There are tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. Further, the positive electrode current collector 201 has various shapes such as foil, plate (sheet), net, columnar, coil, punching metal, expanded metal, porous and non-woven fabric. It can be used as appropriate. Further, the positive electrode current collector 201 may have fine irregularities on the surface in order to improve the adhesion to the active material layer. Coating layer (to reduce contact resistance and improve adhesion
An undercoat) may be provided. The undercoat can be formed of carbon or metal, or a mixed layer of them and a polymer. Further, the positive electrode current collector 201 has a thickness of 5 μm or more and 30 μm.
It is preferable to use the one of m or less.

The active material layer 202 contains a positive electrode active material. The active material refers only to substances and particles involved in the insertion and desorption of ions, which are carriers, but in the present specification and the like, in addition to the material that is originally the "active material",
A layer containing a conductive additive or a binder is also called an active material layer.

As the positive electrode active material, a material capable of inserting and removing lithium ions can be used.
For example, olivine-type crystal structure, layered rock salt-type crystal structure, or spinel-type crystal structure, N.
Examples thereof include materials having an ASICON type crystal structure.

For example, as the positive electrode active material, LiFeO ₂ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O
₄ , V ₂ O ₅ , Cr ₂ O ₅ , MnO ₂ , and other compounds can be used as materials.

Examples of the lithium-containing compound having an olivine structure include transition metal lithium phosphate, for example, the general formula L.
Examples thereof include composite oxides represented by iMPO ₄ (M is one or more of Fe (II), Mn (II), Co (II), and Ni (II)). As a typical example of the general formula LiMPO ₄ , LiFe
PO ₄ , LiNiPO ₄ , LiCoPO ₄ , LiMnPO ₄ , LiFe _a Ni _b PO ₄ ,
LiFe _a Co _b PO ₄ , LiFe _a Mn _b PO ₄ , LiNi _a Co _b PO ₄ , LiNi
_a Mn _b PO ₄ (a + _b is 1 or less, 0 <a <1, 0 < _b <1), LiFe _c Nid Coe
PO ₄ , LiFe _c Ni _d Mn _e PO ₄ , LiNi _c Co _d Mn _e PO ₄ (c + d + e is 1 or less, 0 <c <1, 0 <d <1, 0 <e <1), LiFe _f Ni _g Co _h Mn _i PO ₄
(F + g + h + i is 1 or less, 0 <f <1, 0 <g <1, 0 <h <1, 0 <i <1) and the like.

In particular, LiFePO ₄ is preferable because it satisfies the requirements for the positive electrode active material in a well-balanced manner, such as safety, stability, high capacity density, high potential, and the presence of lithium ions extracted during initial oxidation (charging).

Examples of the lithium-containing compound having a layered rock salt type crystal structure include lithium cobalt oxide (LiCoO ₂ ), LiNiO ₂ , LiMnO ₂ , Li ₂ MnO ₃ , and LiNi _0.8 C.
o _0.2 O ₂ etc. NiCo system (general formula is LiNi _x Co _1-x O ₂ (0 <x <1)),
NiMn system such as LiNi _0.5 Mn _0.5 O ₂ (general formula is LiNi _x Mn _1-x O ₂ (general formula is LiNi x Mn 1-x O 2)
0 <x <1)), LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and other NiMnCo-based (NMC)
Also called. The general formula is LiNi _x Mn _y Co _1-x-y O ₂ (x> 0, y> 0, x + y <
1)) can be mentioned. Furthermore, Li (Ni _0.8 Co _0.15 Al _0.05 ) O ₂ and Li
₂ MnO ₃ -LiMO ₂ (M = Co, Ni, Mn) and the like can also be mentioned.

In particular, LiCoO ₂ has a large capacity and is more stable in the atmosphere than LiNiO ₂ , Li.
It is preferable because it has advantages such as thermal stability as compared with NiO ₂ .

Examples of the lithium-containing compound having a spinel-type crystal structure include LiMn ₂ O ₄ and the like.
Examples thereof include Li _{1 + x} Mn _2-x O ₄ , Li (MnAl) ₂ O ₄ , LiMn _1.5 Ni _0.5 O ₄ .

When a small amount of lithium nickelate (LiNiO ₂ or LiNi _1-x MO ₂ (M = Co, Al, etc.)) is mixed with a lithium-containing compound having a spinel-type crystal structure containing manganese such as LiMn ₂ O ₄ , manganese is produced. It is preferable because it has advantages such as suppressing the elution of lithium and suppressing the decomposition of the electrolytic solution.

Further, as the positive electrode active material, the general formula Li _(2-j) MSiO ₄ (M is Fe (II), Mn.
(II), one or more of Co (II) and Ni (II), and a compound represented by 0 ≦ j ≦ 2) can be used. As a typical example of the general formula Li _(2-j) MSiO ₄ , Li _(2-j) F
eSiO ₄ , Li _(2-j) NiSiO ₄ , Li _(2-j) CoSiO ₄ , Li ₍ 2-j)
₎ MnSiO ₄ , Li _(2-j) Fe _k Ni _l SiO ₄ , Li _(2-j) Fe _{k Col} S
iO ₄ , Li _(2-j) Fe _k Mn _l SiO ₄ , Li _(2-j) Ni _{k Core} SiO ₄ ,
Li _(2-j) Nik Mn _l SiO ₄ ( _k + l is 1 or less, 0 <k <1, 0 <l <1), L
i _(2-j) Fe _m Ni _n Co _q SiO ₄ , Li _(2-j) Fe _m Ni _n Mn _q SiO ₄
, Li _(2-j) Ni _m Con _n Mn _q SiO ₄ (m + n + q is 1 or less, 0 <m <1, 0 <
n <1, 0 <q <1), Li _(2-j) Ferr Nis Cot Mn _u SiO ₄ ( _r + _s + _t )
Examples of + u include 1 or less, 0 <r <1, 0 <s <1, 0 <t <1, 0 <u <1), and the like.

Further, as the positive electrode active material, A _x M ₂ (XO ₄ ) ₃ (A = Li, Na, Mg, M = Fe, M).
A Nashicon type compound represented by the general formula of n, Ti, V, Nb, Al, X = S, P, Mo, W, As, Si) can be used. As a pear-con type compound, Fe ₂ (MnO ₄ )
₃ , Fe ₂ (SO ₄ ) ₃ , Li ₃ Fe ₂ (PO ₄ ) ₃ , and the like can be mentioned. Further, as the positive electrode active material, a compound represented by the general formula of Li ₂ MPO ₄ F, Li ₂ MP ₂ O ₇ , Li ₅ MO ₄ (M = Fe, Mn), NaF ₃ , FeF ₃ , etc. Fluoride, TiS ₂ , M
Metallic chalcogenides (sulfides, seleniums, tellurides) such as oS ₂ , lithium-containing composite materials having a reverse spinel-type crystal structure such as LiMVO ₄ , vanadium oxide (V ₂ O ₅ ,
Materials such as V ₆ O ₁₃ , LiV ₃ O ₈ ), manganese oxide, and organic sulfur can be used.

When the carrier ion is an alkali metal ion other than lithium ion, an alkaline earth metal ion, a beryllium ion, or a magnesium ion, the above lithium compound is used as a positive electrode active material in place of an alkali metal (for example, sodium). , Potassium, etc.), alkaline earth metals (berylium, magnesium, calcium, strontium, barium, etc.) may be used.

Further, graphene added to the positive electrode active material layer 202 as a conductive auxiliary agent is formed by performing a reduction treatment on graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less.

Graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less can be produced by oxidizing graphite.

A sulfuric acid solution of potassium permanganate, a hydrogen peroxide solution, or the like is added to the graphite powder to cause an oxidation reaction to prepare a dispersion containing graphite oxide. In graphite oxide, functional groups such as epoxy group, carbonyl group, carboxyl group and hydroxyl group are bonded by oxidation of carbon of graphite. Therefore, the interlayer distance of the plurality of graphenes is longer than that of graphite, and it becomes easy to slice the graphene by separating the layers. Next, by applying ultrasonic vibration to the dispersion liquid containing graphite oxide, graphite oxide having a long interlayer distance can be cleaved to separate graphene oxide, and a dispersion liquid containing graphene oxide can be produced. and,
By removing the solvent from the dispersion liquid containing graphene oxide, powdered graphene oxide can be obtained.

Here, graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less can be formed by appropriately adjusting the amount of an oxidizing agent such as potassium permanganate. That is,
By increasing the amount of the oxidant with respect to the graphite powder, the degree of oxidation of graphene oxide (weight ratio of oxygen to carbon) can be increased. Therefore, the amount of the oxidizing agent with respect to the graphite powder as a raw material may be determined according to the amount of graphene oxide to be produced.

The production of graphene oxide is not limited to the method using a sulfuric acid solution of potassium permanganate, and for example, a method using nitric acid, potassium chlorate, sodium nitrate or the like, or a method for producing graphene oxide other than these may be appropriately used. good.

Further, the fragmentation of graphite oxide may be performed by addition of ultrasonic vibration, irradiation with microwaves, radio waves, or thermal plasma, or addition of physical stress.

The produced graphene oxide has an epoxy group, a carbonyl group, a carboxyl group, a hydroxyl group and the like. Since the graphene oxide has these substituents moderately, oxygen in the functional group is negatively charged in a polar solvent typified by NMP, interacts with NMP, and repels different graphene oxides. , Hard to aggregate. Therefore, graphene oxide tends to be uniformly dispersed in the polar solvent.

The length of one side of graphene oxide (also referred to as flake size) is 50 nm or more and 100.
It is μm or less, preferably 800 nm or more and 20 μm or less. In particular, when the flake size is smaller than the average particle size of the granular positive electrode active material, it becomes difficult to make surface contact with a plurality of positive electrode active materials and it becomes difficult to connect the graphenes to each other. It becomes difficult to improve the sex.

The plurality of granular positive electrode active materials are coated with a plurality of graphenes. A single sheet of graphene connects to a plurality of granular positive electrode active materials. In particular, since graphene is in the form of a sheet, it can be surface-contacted so as to wrap a part of the surface of the granular positive electrode active material. Unlike granular conductive auxiliaries such as acetylene black, which make point contact with the positive electrode active material, graphene enables surface contact with low contact resistance, so the granular positive electrode does not increase the amount of conductive auxiliaries. It is possible to improve the electrical conductivity between the active material and graphene.

In addition, multiple graphenes come into surface contact with each other. This is because graphene oxide, which has sufficient dispersibility in a polar solvent, is used for the formation of graphene. Since the solvent is volatilized and removed from the dispersion medium containing uniformly dispersed graphene oxide and the graphene oxide is reduced to graphene, the graphene remaining in the positive electrode active material layer 202 partially overlaps and comes into surface contact with each other. The dispersion forms a path of electrical conduction.

Graphene does not necessarily overlap with other graphene only on the surface of the positive electrode active material layer 202, and a part of graphene is formed so as to be arranged three-dimensionally, such as sneaking into the positive electrode active material layer 202. There is. In addition, since graphene is an extremely thin film (sheet) composed of a single layer of carbon molecules or a laminate of these, it covers and contacts a part of the surface of each granular positive electrode active material so as to trace the surface. The portion that is not in contact with the positive electrode active material is bent, wrinkled, or stretched and stretched among a plurality of granular positive electrode active materials.

In the vertical cross section of the positive electrode active material layer 202, the sheet-shaped graphene is dispersed substantially uniformly inside the positive electrode active material layer 202. Similar to the description of the upper surface of the positive electrode active material layer 202,
Since the plurality of graphenes are formed so as to enclose or cover the plurality of granular positive electrode active materials, they come into surface contact with each other. In addition, graphenes come into surface contact with each other to form a network of electrical conduction by a plurality of graphenes.

The plurality of sheet-shaped graphenes are three-dimensionally dispersed inside the positive electrode active material layer 202, and these are in surface contact with each other to form a three-dimensional electrically conductive network. again,
Each graphene is coated with a plurality of granular positive electrode active materials and comes into surface contact with each other. Therefore, the bond between the positive electrode active materials is maintained. Further, graphene obtained by reducing graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less has high conductivity. From the above, by using graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less as a raw material and using graphene reduced after forming a paste as a conductive auxiliary agent, positive electrode activity having high electrical conductivity can be obtained. The material layer 202 can be formed.

Further, since it is not necessary to increase the amount of the conductive auxiliary agent added in order to increase the contact points between the positive electrode active material and graphene, the ratio of the positive electrode active material in the positive electrode active material layer 202 can be increased. As a result, the discharge capacity of the secondary battery can be increased.

The average particle size of the primary particles of the granular positive electrode active material is 500 nm or less, preferably 50 nm or more 5
It is preferable to use one having a diameter of 00 nm or less. In order to make surface contact with multiple of these granular positive electrode active materials,
Graphene has a side length of 50 nm or more and 100 μm or less, preferably 800 nm or more and 20.
It is preferably μm or less.

The binder contained in the positive electrode active material layer 202 includes typical polyvinylidene fluoride (PVdF), polyimide, polytetrafluoroethylene, polyvinyl chloride, ethylene propylene diene polymer, and styrene-butadiene rubber. , Acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethylmethacrylate, polyethylene, nitrocellulose and the like can be used.

As shown in the present embodiment, graphene having a particle size larger than the average particle size of the granular positive electrode active material is dispersed in the positive electrode active material layer 202 to such an extent that it comes into surface contact with one or more of other adjacent graphenes. By surface contact so as to wrap a part of the surface of the granular positive electrode active material, a positive electrode for a secondary battery including a positive electrode active material layer having a high filling amount and a high density is provided with a small amount of a conductive auxiliary agent. can do.

This embodiment can be implemented in combination with other embodiments as appropriate.

(Embodiment 3)
Next, a positive electrode paste is prepared using the above-mentioned positive electrode active material, conductive auxiliary agent, binder, and dispersion medium, and the positive electrode paste is applied onto the positive electrode current collector 201 in a reducing atmosphere or under reduced pressure. A method for producing the positive electrode 200 including the positive electrode active material layer 202 by drying will be described.

NMP is prepared as a dispersion medium, and graphene oxide having an oxygen weight ratio of 2.5 or more and 4 or less to carbon described in the first and second embodiments and lithium iron phosphate as a positive electrode active material are used in the NMP. Disperse. The amount of graphene oxide is 2w with respect to the total amount of positive electrode paste.
If it is less than t%, the conductivity is lowered when the positive electrode active material layer 202 is formed. When the amount of graphene oxide exceeds 10 wt%, the viscosity of the positive electrode paste increases, depending on the particle size of the positive electrode active material. Further, during the drying step after applying the positive electrode paste to the positive electrode current collector 201, convection occurs in the positive electrode paste due to heating, and light and thin graphene oxide moves and aggregates to form the positive electrode active material layer 202. There is a risk of cracking or the positive electrode active material layer 202 peeling off from the positive electrode current collector 201. Therefore, the amount of graphene oxide may be 2 wt% or more and 10 wt% or less with respect to the positive electrode paste (total weight of the positive electrode active material, the conductive auxiliary agent, and the binder). Since graphene oxide is reduced by a subsequent heat treatment step to become graphene and its weight is almost halved, the weight ratio in the positive electrode active material layer 202 is 1 wt% or more and 5 wt% or less.

The average particle size of the primary particles of lithium iron phosphate should be 20 nm or more and 500 nm or less. The amount of lithium iron phosphate to be added may be 85 wt% or more, and may be, for example, 85 wt% or more and 93 wt% or less with respect to the total amount of the positive electrode paste.

In addition, carbohydrates such as glucose may be mixed at the time of firing of lithium iron phosphate, and the particles of lithium iron phosphate may be coated with carbon. This treatment enhances conductivity.

Next, by kneading these mixture pastes (kneading in a highly viscous state), graphene oxide and lithium iron phosphate can be unaggregated. Also, graphene oxide is
Since it has a functional group, oxygen in the functional group is negatively charged in a polar solvent, so that it is difficult for different graphene oxides to aggregate with each other. In addition, graphene oxide has a strong interaction with lithium iron phosphate. Therefore, graphene oxide can be more uniformly dispersed in lithium iron phosphate.

Next, PVdF is added as a binder to these mixtures. The amount of PVdF may be set according to the amount of graphene oxide and lithium iron phosphate, and is 1w with respect to the positive electrode paste.
It may be added in an amount of t% or more and 5 wt% or less. By adding a binder in a state where graphene oxide is uniformly dispersed so as to be in surface contact with a plurality of positive electrode active material particles, the positive electrode active material and graphene oxide are bound while maintaining the dispersed state. You can wear it. Further, depending on the ratio of lithium iron phosphate and graphene oxide, it is not necessary to add a binder, but when a binder is added, the strength of the positive electrode can be improved.

Next, NMP can be added to these mixtures until they have a predetermined viscosity and kneaded to prepare a positive electrode slurry. By producing a positive electrode slurry in the above steps,
It is possible to prepare a positive electrode slurry in which the kneaded state of graphene oxide, the positive electrode active material, and the binder is uniform.

Next, the positive electrode paste is applied onto the positive electrode current collector 201.

Next, the positive electrode paste applied on the positive electrode current collector 201 is dried. The drying process is 60 ° C.
This is done by evaporating NMP by heating at ~ 170 ° C. for 1 minute to 10 hours. The atmosphere is not particularly limited.

Next, the positive electrode paste is dried in a reducing atmosphere or under reduced pressure. By heating in a reducing atmosphere or under reduced pressure at a temperature of 130 ° C. to 200 ° C. for 10 hours to 30 hours, NMP and water remaining in the positive electrode paste are evaporated, and oxygen contained in graphene oxide is desorbed. As a result, graphene oxide can be converted into graphene. All oxygen contained in graphene oxide is not desorbed, and some oxygen may remain in graphene.

By the above steps, the positive electrode 200 including the positive electrode active material layer 202 in which graphene is uniformly dispersed in the positive electrode active material can be produced. After the drying step, a pressurizing step may be performed on the positive electrode 200.

As described in the present embodiment, the positive electrode active material is added to the dispersion medium in which graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less is dispersed, and kneaded to obtain the positive electrode active material. Graphene oxide can be uniformly dispersed therein. By adding the binder in a state where the graphene oxide is dispersed so as to be in contact with the plurality of positive electrode active material particles, the binder is added without inhibiting the contact between the graphene oxide and the plurality of positive electrode active material particles. Can be uniformly dispersed. Further, graphene obtained by reducing graphene oxide having a weight ratio of oxygen to carbon of 2.5 or more and 4 or less has high conductivity. By using the positive electrode paste produced in this way,
It is possible to produce a positive electrode containing a high-density positive electrode active material layer with a high filling amount of the positive electrode active material. Further, by manufacturing a battery using the positive electrode, a high-capacity secondary battery can be manufactured. Furthermore, since the sheet-shaped graphene can be maintained in contact with a plurality of positive electrode active materials by the binder, peeling between the positive electrode active material and graphene can be suppressed, so that the cycle characteristics are good. It is possible to manufacture various secondary batteries.

This embodiment can be implemented in combination with other embodiments as appropriate.

(Embodiment 4)
In the present embodiment, the structure of the secondary battery and the method for manufacturing the secondary battery will be described with reference to FIGS. 2 and 3.

FIG. 2A is an external view of a coin-type (single-layer flat type) secondary battery, and FIG. 2B is a cross-sectional view thereof.

In the coin-type secondary battery 300, a positive electrode can 301 that also serves as a positive electrode terminal and a negative electrode can 302 that also serves as a negative electrode terminal are insulated and sealed with a gasket 303 that is made of polypropylene or the like.
The positive electrode 304 is a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector 305.
Is formed by. Further, the negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector 308. Positive electrode active material layer 306 and negative electrode active material layer 309
There is a separator 310 and an electrolyte (not shown) between the two.

As the positive electrode 304, the positive electrode 200 shown in the second and third embodiments can be used.

The negative electrode 307 is formed by forming the negative electrode active material layer 309 on the negative electrode current collector 308 by a CVD method, a sputtering method, or a coating method.

The negative electrode current collector 308 is not particularly limited as long as it exhibits high conductivity without causing a significant chemical change in the power storage device. For example, copper, aluminum, stainless steel, gold, platinum, zinc, iron,
Metals such as nickel, titanium, tantalum and manganese, alloys thereof, sintered carbon and the like can be used. Further, copper or stainless steel may be coated with carbon, nickel, titanium or the like. Further, an aluminum alloy to which an element for improving heat resistance such as silicon, neodymium, scandium, and molybdenum is added can be used. Further, it may be formed of a metal element that reacts with silicon to form silicide. Metallic elements that react with silicon to form silicides include zirconium, titanium, hafnium, vanadium, niobium, and so on.
There are tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. Further, the current collector 308 has various shapes such as foil shape, plate shape (sheet shape), net shape, columnar shape, coil shape, punching metal shape, expanded metal shape, porous shape and non-woven fabric as appropriate. Can be used. Further, the negative electrode current collector 308 may have fine irregularities on the surface in order to improve the adhesion to the active material layer. A coating layer (undercoat) may be provided in order to reduce contact resistance and improve adhesion. The undercoat can be formed of carbon or metal, or a mixed layer of them and a polymer. Further, it is preferable to use a negative electrode current collector 308 having a thickness of 5 μm or more and 30 μm or less.

As the negative electrode active material, a material capable of dissolving / precipitating lithium or inserting / removing lithium ions can be used, and examples thereof include lithium metal, carbon-based materials, and alloy-based materials.

Lithium metal has a low redox potential (-3.405V with respect to standard hydrogen electrode) and a large specific capacity per weight and volume (3860mAh / g and 2062mAh / cm ³ respectively).
) Therefore, it is preferable.

Examples of the carbon-based material include graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black and the like.

Examples of graphite include artificial graphite such as mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite, and natural graphite such as spheroidized natural graphite.

Graphite exhibits as low a potential as lithium metal when lithium ions are inserted into graphite (during the formation of a lithium-graphite intercalation compound) (0.1-0.3 V vs. Li / Li ⁺ ). This allows the lithium-ion battery to exhibit a high operating voltage. Further, graphite is preferable because it has advantages such as relatively high capacity per unit volume, small volume expansion, low cost, and high safety as compared with lithium metal.

As the negative electrode active material, an alloy-based material capable of performing a charge / discharge reaction by an alloying / dealloying reaction with a lithium metal can also be used. For example, Al, Si, Ge, Sn, Pb, S
Examples thereof include materials containing at least one of b, Bi, Ag, Zn, Cd, In, Ga and the like. Such elements have a large capacity with respect to carbon, and silicon in particular has a theoretical capacity of 4200 m.
It is dramatically higher at Ah / g. Therefore, it is preferable to use silicon as the negative electrode active material. Examples of alloy-based materials using such elements include SiO, Mg ₂ Si, Mg ₂ Ge, and the like.
SnO, SnO ₂ , Mg ₂ Sn, SnS ₂ , V ₂ Sn ₃ , FeSn ₂ , CoSn ₂ , Ni
₃ Sn ₂ , Cu ₆ Sn ₅ , Ag ₃ Sn, Ag ₃ Sb, Ni ₂ MnSb, CeSb ₃ , La
Examples thereof include Sn ₃ , La ₃ Co ₂ Sn ₇ , CoSb ₃ , InSb, and SbSn.

Further, as the negative electrode active material, titanium dioxide (TiO ₂ ) and lithium titanium oxide (Li ₄ T) are used.
i ₅ O ₁₂ ), Lithium-graphite intercalation compound (Li _x C ₆ ), Niobium pentoxide (Nb ₂ O ₅ )
, Tungsten oxide (WO ₂ ), molybdenum oxide (MoO ₂ ) and other oxides can be used.

Further, as the negative electrode active material, Li _{3 -x} M _x N (M = Co, Ni, Cu) having a Li 3N type structure, which is a double nitride of lithium and a transition metal, can be used. For example, Li _2.6
Co _0.4 N ₃ shows a large charge / discharge capacity (900 mAh / g) and is preferable.

When lithium and transition metal compound nitrides are used, lithium ions are contained in the negative electrode active material.
As the positive electrode active material, it is preferable because it can be combined with a material such as V ₂ O ₅ and Cr ₃ O ₈ which does not contain lithium ions. Even when a material containing lithium ions is used as the positive electrode active material, a double nitride of lithium and a transition metal can be used by desorbing the lithium ions in advance.

Further, a material that causes a conversion reaction can also be used as a negative electrode active material. For example, a transition metal oxide that does not alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. Further, as the material in which the conversion reaction occurs, Fe ₂ O ₃ , CuO, Cu ₂ O, RuO ₂ , Cr ₂ O
Oxides such as ₃ mag, sulfides such as CoS _0.89 , NiS, CuS, Zn ₃ N ₂ , Cu ₃ N, G
Nitrides such as e ₃ N ₄ and phosphides such as NiP ₂ , FeP ₂ and CoP ₃ , FeF ₃ and BiF ₃
There are fluorides and the like. Since the potential of the fluoride is high, it may be used as a positive electrode active material.

When the negative electrode active material layer 309 is formed by the coating method, a conductive auxiliary agent or a binder is added to the negative electrode active material to prepare a negative electrode paste, which is applied onto the negative electrode current collector 308 and dried. Just let me do it.

When the negative electrode active material layer 309 is formed by using silicon as the negative electrode active material, it is preferable to form graphene on the surface of the negative electrode active material layer 309. Since the volume of silicon changes significantly due to the occlusion and release of carrier ions in the charge / discharge cycle, the adhesion between the negative electrode current collector 308 and the negative electrode active material layer 309 deteriorates, and the battery characteristics deteriorate due to charge / discharge. It ends up. Therefore, by forming graphene on the surface of the negative electrode active material layer 309 containing silicon, the adhesion between the negative electrode current collector 308 and the negative electrode active material layer 309 is maintained even if the volume of silicon changes in the charge / discharge cycle. It is preferable because the deterioration can be suppressed and the deterioration of the battery characteristics is reduced.

The graphene formed on the surface of the negative electrode active material layer 309 can be formed by reducing graphene oxide in the same manner as in the method for producing a positive electrode. The graphene oxide is the first embodiment.
Graphene oxide described in the above can be used.

A method of forming graphene oxide on the negative electrode active material layer 309 by using an electrophoresis method will be described with reference to FIG. 3 (A).

FIG. 3A is a cross-sectional view for explaining the electrophoresis method. In the container 401, the first embodiment
Dispersion liquid in which graphene oxide described in the above is dispersed in a dispersion medium (hereinafter referred to as graphene oxide dispersion liquid 4).
It's called 02. ) Is included. Further, the object to be formed 403 is provided in the graphene oxide dispersion liquid 402, and this is used as an anode. Further, the conductor 4 serving as a cathode in the graphene oxide dispersion liquid 402
04 is provided. The object to be formed 403 is a negative electrode current collector 308 and a negative electrode active material layer 309 formed on the negative electrode current collector 308. Further, the conductor 404 may be a conductive material, for example, a metal material or an alloy material.

By applying an appropriate voltage between the anode and the cathode, a layer of graphene oxide is formed on the surface of the object to be formed 403, that is, the surface of the negative electrode active material layer 309. This is because graphene oxide is negatively charged in the polar solvent as described above, and therefore, when a voltage is applied, the negatively charged graphene oxide is attracted to the anode and adheres to the object to be formed 403. The negative charge of graphene oxide is derived from the fact that hydrogen ions are desorbed from the substituents such as hydroxyl group and carboxyl group of graphene oxide, and the substance is neutralized by binding to the substituent. The applied voltage does not have to be constant. Further, by measuring the amount of electric charge flowing between the anode and the cathode, the thickness of the graphene oxide layer adhering to the object can be estimated.

The voltage applied between the anode and the cathode is preferably in the range of 0.5V to 2.0V. More preferably, it is 0.8 V to 1.5 V. For example, when the voltage applied between the anode and the cathode is 1 V, it is difficult to form an oxide film which can be formed by the principle of anodization between the object to be formed and the graphene oxide layer.

Once the graphene oxide of the required thickness is obtained, the workpiece 403 is added to the graphene oxide dispersion 40.
Pull up from 2 and dry.

In the electrodeposition of graphene oxide by electrophoresis, it is rare that graphene oxide is further laminated on the portion already covered with graphene oxide. This is because the conductivity of graphene oxide is sufficiently low. On the other hand, graphene oxide is preferentially laminated on the portion not yet covered with graphene oxide. Therefore, the thickness of graphene oxide formed on the surface of the object to be formed 403 is practically uniform.

The time for electrophoresis (time for applying voltage) may be longer than the time required for the surface of the object to be formed 403 to be covered with graphene oxide, for example, 0.5 minutes or more and 30 minutes or less, preferably 5. It may be more than 20 minutes and less than 20 minutes.

By using the electrophoresis method, the ionized graphene oxide can be electrically transferred to the active material, so that the graphene oxide can be uniformly provided even if the surface of the negative electrode active material layer 309 has irregularities. Is.

Next, a reduction treatment is performed to desorb a part of oxygen from the formed graphene oxide. As the reduction treatment, the reduction treatment by heating described in the second embodiment using graphene may be performed, but here, the electrochemical reduction treatment (hereinafter referred to as electrochemical reduction) will be described.

The electrochemical reduction of graphene oxide is a reduction using electric energy, unlike the reduction by heat treatment. As shown in FIG. 3B, a negative electrode having graphene oxide provided on the negative electrode active material layer 309 is used as the conductor 407 to form a closed circuit, and the potential at which the reduction reaction of the graphene oxide occurs in the conductor 407. Or, the potential for reducing the graphene oxide is supplied, and the graphene oxide is reduced to graphene. In the present specification, the potential at which the reduction reaction of graphene oxide occurs or the potential at which the graphene oxide is reduced is referred to as a reduction potential.

The reduction method of graphene oxide will be specifically described with reference to FIG. 3 (B). The container 405 is filled with the electrolytic solution 406, and the conductor 407 having graphene oxide and the counter electrode 408 are inserted therein and immersed. Next, a conductor 407 having graphene oxide is used as a working electrode, and at least a counter electrode 408 and an electrolytic solution 406 are used to form an electrochemical cell (open circuit), and the conductor 40 is formed.
The reduction potential of graphene oxide is supplied to the potential of 7 (working electrode), and the graphene oxide is reduced to graphene. The reduction potential to be supplied is the reduction potential when the counter electrode 408 is used as a reference.
Alternatively, a reference electrode is provided in the electrochemical cell, and the reduction potential is used with the reference electrode as a reference. For example, when the counter electrode 408 and the reference electrode are lithium metals, the reduction potential to be supplied is a reduction potential (vs. Li / Li ⁺ ) based on the redox potential of the lithium metal. By this step, a reduction current flows through the electrochemical cell (closed circuit) when graphene oxide is reduced. Therefore, in order to confirm the reduction of graphene oxide, the reduction current may be continuously confirmed, and the graphene oxide is in a state where the reduction current is below a certain value (a state in which the peak corresponding to the reduction current disappears). It may be in a reduced state (a state in which the reduction reaction is completed).

Further, when controlling the potential of the conductor 407, not only the potential of the conductor 407 is fixed below the reduction potential of graphene oxide, but also the reduction potential of graphene oxide may be included in the sweep, and the sweep may be performed by cyclic voltammetry. It may be repeated periodically like a metric. In addition, the conductor 4
There is no limit to the sweep speed of the potential of 07. When sweeping the potential of the conductor 407, it may be swept from the high potential side to the low potential side, or from the low potential side to the high potential side.

The reduction potential of graphene oxide varies slightly depending on the composition of graphene oxide (presence or absence of functional groups, etc.) and the potential control method (sweep speed, etc.), but is approximately 2.0 V (vs. Li / L).
i ⁺ ). Specifically, the potential of the conductor 407 may be controlled in the range of 1.6 V or more and 2.4 V or less (vs. Li / Li ⁺ ).

By the above steps, graphene can be formed on the conductor 407. When the electrochemical reduction treatment is performed, the proportion of ^double -bonded carbon-carbon bonds, which are sp2 bonds, increases as compared with the graphene formed by the heat treatment. Therefore, the highly conductive graphene is used as the negative electrode active material layer. It can be formed on 309.

After forming graphene on the conductor 407, lithium may be pre-doped into the negative electrode active material layer 309 via graphene. As a lithium predoping method, a lithium layer may be formed on the surface of the negative electrode active material layer 309 by a sputtering method. Alternatively, by providing a lithium foil on the surface of the negative electrode active material layer 309, lithium can be pre-doped into the negative electrode active material layer 309.

As the separator 310, an insulator such as cellulose (paper) or polypropylene or polyethylene provided with holes can be used.

As the electrolytic solution, a material having carrier ions is used as the electrolyte. Typical examples of electrolytes include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF ₆ , and Li (C ₂ F ₅ SO ₂ ) ₂ .
There are lithium salts such as N.

When the carrier ion is an alkali metal ion other than lithium ion, alkaline earth metal ion, beryllium ion, or magnesium ion, the above lithium salt as an electrolyte uses an alkali metal (for example, sodium or potassium) instead of lithium. Etc.), alkaline earth metals (eg, calcium, strontium, barium, etc.), beryllium, or magnesium may be used.

Further, as the solvent of the electrolytic solution, a material capable of transferring carrier ions is used. As the solvent of the electrolytic solution, an aprotic organic solvent is preferable. Typical examples of the aprotic organic solvent include ethylene carbonate (EC), propylene carbonate, dimethyl carbonate, diethyl carbonate (DEC), γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran and the like, and one or more of them may be used. Can be used. Further, by using a gelled polymer material as the solvent of the electrolytic solution, the safety against liquid leakage and the like is enhanced. In addition, the secondary battery can be made thinner and lighter. Typical examples of the polymer material to be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide, polypropylene oxide, and a fluorine-based polymer. In addition, by using one or more flame-retardant and flame-retardant ionic liquids (normal temperature molten salt) as the solvent of the electrolytic solution, the internal temperature rises due to internal short circuit of the secondary battery, overcharging, etc. However, it is possible to prevent the secondary battery from exploding or catching fire.

Further, instead of the electrolytic solution, a solid electrolyte having an inorganic material such as a sulfide type or an oxide type, or P.
A solid electrolyte having a polymer material such as EO (polyethylene oxide) can be used. When a solid electrolyte is used, it is not necessary to install a separator or a spacer. In addition, since the entire battery can be solidified, there is no risk of liquid leakage and safety is dramatically improved.

The positive electrode can 301 and the negative electrode can 302 include metals such as nickel, aluminum, and titanium, which have corrosion resistance against liquids such as electrolytic solutions during charging and discharging of the secondary battery, alloys of the metals, and the metals and others. Alloys with metals (eg, stainless steel, etc.), laminates of the metal, laminates of the metal with the alloys mentioned above (eg, stainless steel \ aluminum, etc.), laminates of the metal with other metals (eg, nickel \ iron \). Nickel, etc.) can be used. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

The negative electrode 307, the positive electrode 304, and the separator 310 are impregnated into the electrolyte, and as shown in FIG. 2B, the positive electrode 304, the separator 310, the negative electrode 307, and the negative electrode can 302 are laminated in this order with the positive electrode can 301 facing down. , The positive electrode can 301 and the negative electrode can 302 are crimped via the gasket 303 to manufacture a coin-shaped secondary battery 300.

Next, an example of the laminated type secondary battery will be described with reference to FIG.

The laminated type secondary battery 500 shown in FIG. 4 has a positive electrode current collector 501 and a positive electrode active material layer 50.
A positive electrode 503 having 2 and a negative electrode 50 having a negative electrode current collector 504 and a negative electrode active material layer 505.
It has 6, a separator 507, an electrolytic solution 508, and an exterior body 509. Exterior body 509
A separator 507 is installed between the positive electrode 503 and the negative electrode 506 provided inside. Further, the inside of the exterior body 509 is filled with the electrolytic solution 508.

In the laminated type secondary battery 500 shown in FIG. 4, the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for obtaining electrical contact with the outside. Therefore, the positive electrode current collector 5
The 01 and a part of the negative electrode current collector 504 are arranged so as to be exposed to the outside from the exterior body 509.

In the laminated secondary battery 500, the exterior body 509 has a highly flexible metal such as aluminum, stainless steel, copper, and nickel on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, and polyamide. A three-layered laminated film in which a thin film is provided and an insulating synthetic resin film such as a polyamide resin or a polyester resin is provided on the metal thin film as the outer surface of the exterior body can be used. By having such a three-layer structure, the permeation of the electrolytic solution and the gas is blocked, the insulating property is ensured, and the electrolytic solution resistance is also provided.

Next, an example of a cylindrical secondary battery will be described with reference to FIG. Cylindrical secondary battery 6
As shown in FIG. 5A, 00 has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. These positive electrode caps and battery cans (exterior cans) 6
02 is insulated by a gasket (insulating packing) 610.

FIG. 5B is a diagram schematically showing a cross section of a cylindrical secondary battery. Inside the hollow cylindrical battery can 602, a battery element in which a band-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 sandwiched between them is provided. Although not shown, the battery element is wound around the center pin. One end of the battery can 602 is closed and the other end is open. The battery can 602 is provided with a metal such as nickel, aluminum, titanium, etc., which has corrosion resistance against liquids such as an electrolytic solution during charging and discharging of a secondary battery, an alloy of the metal, and an alloy of the metal and another metal. (for example,
It is possible to use a laminate of the metal (eg, stainless steel, etc.), a laminate of the metal and the alloy described above (eg, stainless steel \ aluminum, etc.), a laminate of the metal and another metal (eg, nickel \ iron \ nickel, etc.). can. Inside the battery can 602, the battery element in which the positive electrode, the negative electrode, and the separator are wound is sandwiched between a pair of insulating plates 608 and 609 facing each other. Further, a non-aqueous electrolytic solution (not shown) is injected into the inside of the battery can 602 provided with the battery element. As the non-aqueous electrolyte solution, the same one as the coin-type or laminated type secondary battery can be used.

The positive electrode 604 and the negative electrode 606 may be manufactured in the same manner as the positive electrode and the negative electrode of the coin-shaped secondary battery described above, but since the positive electrode and the negative electrode used for the cylindrical secondary battery are wound, both sides of the current collector It differs in that it forms an active material. The positive electrode 604 has a positive electrode terminal (positive electrode current collector lead) 603.
Is connected, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. A metal material such as aluminum can be used for both the positive electrode terminal 603 and the negative electrode terminal 607. The positive electrode terminal 603 is resistance welded to the safety valve mechanism 612, and the negative electrode terminal 607 is resistance welded to the bottom of the battery can 602. The safety valve mechanism 612 is a PTC element (Positive Tempera).
It is electrically connected to the positive electrode cap 601 via the true Coefficient) 611. The safety valve mechanism 612 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in the internal pressure of the battery exceeds a predetermined threshold value. Further, the PTC element 6
Reference numeral 11 denotes a heat-sensitive resistance element whose resistance increases when the temperature rises, and the increase in resistance limits the amount of current to prevent abnormal heat generation. The PTC element is barium titanate (Ba).
TiO ₃ ) -based semiconductor ceramics and the like can be used.

In the present embodiment, as the secondary battery, a coin-shaped, laminated-type, and cylindrical secondary battery is shown, but other sealed secondary batteries, square secondary batteries, and other secondary batteries having various shapes are shown. The next battery can be used. In addition, a structure in which a plurality of positive electrodes, negative electrodes, and separators are laminated, positive electrodes, negative electrodes,
And the structure may be such that the separator is wound.

As the positive electrode of the secondary battery 300, the secondary battery 500, and the secondary battery 600 shown in the present embodiment, the positive electrode according to one aspect of the present invention is used. Therefore, the secondary battery 300, the secondary battery 500,
The discharge capacity of the secondary battery 600 can be increased.

[Thin secondary battery]
FIG. 6A shows a thin secondary battery as an example of the power storage device. FIG. 6A shows an example of a thin secondary battery. If the thin secondary battery is configured to have flexibility, the secondary battery can also be bent according to the deformation of the electronic device if it is mounted on an electronic device having at least a part of the flexible portion. ..

FIG. 6 shows an external view of the thin secondary battery 500. 7 (A) and 7 (B) show the A1-A2 cross section and the B1-B2 cross section shown by the alternate long and short dash line in FIG. Thin secondary battery 500
Is a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, and a negative electrode current collector 50.
A negative electrode 506 having 4 and a negative electrode active material layer 505, a separator 507, and an electrolytic solution 508.
And an exterior body 509. A separator 507 is installed between the positive electrode 503 and the negative electrode 506 provided in the exterior body 509. Further, the inside of the exterior body 509 is filled with the electrolytic solution 508.

At least one of the negative electrode 506 and the positive electrode 503 contains graphene oxide, which is one aspect of the present invention.

FIG. 6B shows an example of welding a current collector to a lead electrode. As an example, an example of welding the positive electrode current collector 501 to the positive electrode lead electrode 510 is shown. The positive electrode current collector 501 is welded to the positive electrode lead electrode 510 in the welding region 512 by using ultrasonic welding or the like. Further, since the positive electrode current collector 501 has the curved portion 513 shown in FIG. 6B, it is possible to relieve the stress generated by applying an external force after the production of the secondary battery 500, and the secondary battery. The reliability of 500 can be increased.

In the thin secondary battery 500 shown in FIGS. 6 and 7, the positive electrode lead electrode 510 and the negative electrode lead electrode 511 are ultrasonically bonded to the positive electrode current collector 501 or the negative electrode current collector 504 to form the positive electrode lead electrode 510 and the negative electrode lead electrode 510. The negative electrode lead electrode 511 is exposed to the outside. Further, the positive electrode current collector 501 and the negative electrode current collector 504 can also serve as terminals for obtaining electrical contact with the outside. In that case, the positive electrode current collector 501 and the negative electrode current collector 5 are not used.
A part of 04 may be arranged so as to be exposed to the outside from the exterior body 509.

Further, although the positive electrode lead electrode 510 and the negative electrode lead electrode 511 are arranged on the same side in FIG. 6, as shown in FIG. 7, the positive electrode lead electrode 510 and the negative electrode lead electrode 511 may be arranged on different sides. As described above, in the secondary battery of one aspect of the present invention, the lead electrodes can be freely arranged, so that the degree of freedom in design is high. Therefore, the degree of freedom in designing a product using the secondary battery of one aspect of the present invention can be increased. In addition, the productivity of a product using the secondary battery of one aspect of the present invention can be increased.

In the thin secondary battery 500, the exterior body 509 has a highly flexible metal such as aluminum, stainless steel, copper, and nickel on an inner surface made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, and polyamide. A film having a three-layer structure can be used in which a thin film is provided and an insulating synthetic resin film such as a polyamide resin or a polyester resin is provided on the metal thin film as the outer surface of the exterior body.

Further, in FIG. 6, as an example, the number of pairs of positive electrodes and negative electrodes facing each other is set to 5, but of course.
The set of electrodes is not limited to five, and may be large or small. When the number of electrode layers is large, a secondary battery having a larger capacity can be used. Further, when the number of electrode layers is small, the thickness can be reduced and the secondary battery having excellent flexibility can be obtained.

In the above configuration, the exterior body 509 of the secondary battery can be deformed within a range of a radius of curvature of 10 mm or more, preferably a radius of curvature of 30 mm or more. The film that is the exterior of the secondary battery is 1
In the case of a secondary battery having a laminated structure, which is composed of one or two batteries, the cross-sectional structure of the curved battery is a structure sandwiched between two curves of a film which is an exterior body.

The radius of curvature of the surface will be described with reference to FIG. In FIG. 8A, in the plane 1701 obtained by cutting the curved surface 1700, a part of the curve 1702 which is the shape of the curved surface is approximated to the arc of a circle, the radius of the circle is set to the radius of curvature 1703, and the center of the circle is the curvature. The center is 1704. FIG. 8 (B
) Shows a top view of the curved surface 1700. FIG. 8C shows a cross-sectional view of a curved surface 1700 cut along a plane 1701. When cutting a curved surface with a plane, the radius of curvature of the curve, which is the shape of the curved surface, differs depending on the plane to be cut. Let the radius of curvature of the curve, which is the shape, be the radius of curvature of the surface.

When a secondary battery sandwiching 1805 such as an electrode and an electrolytic solution is curved using two films as an exterior body, the radius of curvature 1802 of the film 1801 on the side closer to the center of curvature 1800 of the secondary battery is from the center of curvature 1800. It is smaller than the radius of curvature 1804 of the film 1803 on the far side (FIG. 9 (A)). When the secondary battery is curved to have an arcuate cross section, compressive stress is applied to the surface of the film near the center of curvature 1800, and tensile stress is applied to the surface of the film far from the center of curvature 1800 (FIG. 9B). By forming a pattern formed by concave portions or convex portions on the surface of the exterior body, even if compressive stress or tensile stress is applied in this way, the influence of strain can be suppressed within an allowable range. Therefore, the secondary battery can be deformed within a range in which the radius of curvature of the exterior body near the center of curvature is 10 mm or more, preferably 30 mm or more.

The cross-sectional shape of the secondary battery is not limited to a simple arc shape, and can be a shape having an arc in part, for example, the shape shown in FIG. 9 (C) or the wavy shape (FIG. 9 (D)). ), S-shaped, etc. When the curved surface of the secondary battery has a shape having a plurality of centers of curvature, the curved surface having the smallest radius of curvature among the radii of curvature at each of the plurality of centers of curvature is closer to the center of curvature of the two exterior bodies. The secondary battery can be deformed within a range in which the radius of curvature of the exterior body is 10 mm or more, preferably 30 mm or more.

In the present embodiment, as the secondary battery, a coin-type, a cylindrical-type, and a thin-type secondary battery are shown, but other sealed-type secondary batteries, square-type secondary batteries, and other secondary batteries having various shapes are shown. Batteries can be used.

(Embodiment 5)
[Example of secondary battery configuration]
10 and 11 show a configuration example of a thin secondary battery. Winding body 993 shown in FIG. 10 (A)
Has a negative electrode 994, a positive electrode 995, and a separator 996.

The wound body 993 is formed by laminating a negative electrode 994 and a positive electrode 995 on top of each other with a separator 996 interposed therebetween, and winding the laminated sheet. A square secondary battery is manufactured by covering the winding body 993 with a square sealing container or the like.

The number of layers of the negative electrode 994, the positive electrode 995, and the separator 996 may be appropriately designed according to the required capacity and the element volume. The negative electrode 994 is connected to a negative electrode current collector (not shown) via one of the lead electrode 997 and the lead electrode 998, and the positive electrode 995 is the lead electrode 9.
It is connected to a positive electrode current collector (not shown) via the other of 97 and the lead electrode 998.

The secondary battery 990 shown in FIGS. 10B and 10C is a wound body 993 described above in a space formed by bonding a film 981 as an exterior body and a film 982 having a recess by thermocompression bonding or the like. Is stored. The winding body 993 includes a lead electrode 997 and a lead electrode 9.
The electrolytic solution is impregnated inside the film 981 having 98 and the film 982 having recesses.

As the film 981 and the film 982 having a recess, a metal material such as aluminum or a resin material can be used. If a resin material is used as the material of the film 981 and the film 982 having recesses, the film 981 and the film 982 having recesses can be deformed when an external force is applied, and a flexible secondary battery can be obtained. Can be made.

Further, although FIGS. 10B and 10C show an example in which two films are used, a space is formed by bending one film, and the above-mentioned winding body 993 is stored in the space. You may.

Further, it is possible to manufacture a flexible power storage device by using a resin material or the like for the exterior body or the sealing container, instead of the power storage device in which only the thin secondary battery has flexibility. However, when the exterior body or the sealing container is made of a resin material, the part to be connected to the outside is made of a conductive material.

For example, FIG. 11 shows an example of another thin secondary battery having flexibility. Winding body 9 in FIG. 11 (A)
Since 93 is the same as that shown in FIG. 10 (A), detailed description thereof will be omitted.

The secondary battery 990 shown in FIGS. 11B and 11C contains the above-mentioned winding body 993 inside the exterior body 991. The winding body 993 has a lead electrode 997 and a lead electrode 998.
And is impregnated with the electrolytic solution inside the exterior bodies 991 and 992. The exterior bodies 991 and 992 are
For example, a metal material such as aluminum or a resin material can be used. Exteriors 991, 9
If a resin material is used as the material of 92, the exterior bodies 991 and 99 are applied when an external force is applied.
2 can be deformed, and a thin secondary battery having flexibility can be produced.
[Structural example of power storage system]
Further, a structural example of the power storage system will be described with reference to FIGS. 12, 13, and 14. Here, the power storage system refers to, for example, a device equipped with a power storage device.

12 (A) and 12 (B) are views showing an external view of the power storage system. The power storage system includes a circuit board 900 and a secondary battery 913. The secondary battery 913 has a label 91.
0 is pasted. Further, as shown in FIG. 12B, the power storage system has a terminal 951 and a terminal 952, and has an antenna 914 and an antenna 915 behind the label 910.

The circuit board 900 has a terminal 911 and a circuit 912. Terminal 911 is terminal 951
, Terminal 952, antenna 914, antenna 915, and circuit 912. note that,
A plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, or the like.

The circuit 912 may be provided on the back surface of the circuit board 900. The antenna 914 and the antenna 915 are not limited to the coil shape, and may be, for example, a linear shape or a plate shape. again,
Antennas such as a plane antenna, an open surface antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may be used. Alternatively, the antenna 914 or the antenna 915 may be a flat conductor. This flat plate-shaped conductor can function as one of the conductors for electric field coupling. That is, the antenna 914 or the antenna 915 may function as one of the two conductors of the capacitor. This makes it possible to exchange electric power not only with an electromagnetic field and a magnetic field but also with an electric field.

The line width of the antenna 914 is preferably larger than the line width of the antenna 915. As a result, the amount of electric power received by the antenna 914 can be increased.

The power storage system includes a layer 91 between the antenna 914 and the antenna 915 and the secondary battery 913.
Has 6. The layer 916 has a function of preventing the electromagnetic field from being shielded by, for example, the secondary battery 913. As the layer 916, for example, a magnetic material can be used. The layer 916 may be used as a shielding layer.

The structure of the power storage system is not limited to FIG.

For example, as shown in FIGS. 13 (A-1) and 13 (A-2), FIGS. 12 (A) and 12 (A).
Of the secondary batteries 913 shown in (B), antennas may be provided on each of the pair of facing surfaces. FIG. 13 (A-1) is an external view seen from one side of the pair of surfaces, and is a view of FIG. 13 (A-1).
A-2) is an external view seen from the other side of the pair of surfaces. The same parts as the power storage system shown in FIGS. 12 (A) and 12 (B) are shown in FIGS. 12 (A) and 12 (B).
The description of the power storage system shown in the above can be appropriately referred to.

As shown in FIG. 13 (A-1), the antenna 914 is provided on one of the pair of surfaces of the secondary battery 913 with the layer 916 interposed therebetween, and as shown in FIG. 13 (A-2), the secondary battery 913 is provided. The antenna 915 is provided on the other side of the pair of surfaces of the above, with the layer 917 interposed therebetween. Layer 917 is, for example, a secondary battery 91.
It has a function of preventing the shielding of the electromagnetic field by 3. As the layer 917, for example, a magnetic material can be used. The layer 917 may be used as a shielding layer.

With the above structure, the sizes of both the antenna 914 and the antenna 915 can be increased.

Alternatively, as shown in FIGS. 13 (B-1) and 13 (B-2), FIGS. 12 (A) and 12 (
Of the secondary batteries 913 shown in B), different antennas may be provided on each of the pair of facing surfaces. FIG. 13 (B-1) is an external view of the pair of surfaces viewed from one side, and is a view of FIG. 13.
(B-2) is an external view seen from the other side of the pair of surfaces. The same parts as the power storage system shown in FIGS. 12 (A) and 12 (B) are shown in FIGS. 12 (A) and 12 (B).
) Can be appropriately referred to in the description of the power storage system.

As shown in FIG. 13 (B-1), the antenna 914 and the antenna 915 are provided on one of the pair of surfaces of the secondary battery 913 with the layer 916 interposed therebetween, and as shown in FIG. 13 (A-2), two. An antenna 918 is provided on the other side of the pair of surfaces of the next battery 913 with the layer 917 interposed therebetween. Antenna 91
Reference numeral 8 has, for example, a function capable of performing data communication with an external device. Antenna 91
For example, an antenna having a shape applicable to the antenna 914 and the antenna 915 can be applied to 8. As a communication method between the power storage system and other devices via the antenna 918, a response method that can be used between the power storage system and other devices such as NFC can be applied.

Or, as shown in FIG. 14 (A), the secondary battery 913 shown in FIGS. 12 (A) and 12 (B).
May be provided with a display device 920. The display device 920 is electrically connected to the terminal 911 via the terminal 919. It is not necessary to provide the label 910 in the portion where the display device 920 is provided. For the same parts as the power storage system shown in FIGS. 12 (A) and 12 (B), the description of the power storage system shown in FIGS. 12 (A) and 12 (B) can be appropriately referred to.

The display device 920 may display, for example, an image showing whether or not charging is in progress, an image showing the amount of stored electricity, and the like. As the display device 920, for example, an electronic paper, a liquid crystal display device, an electroluminescence (also referred to as EL) display device, or the like can be used. For example, the power consumption of the display device 920 can be reduced by using electronic paper.

Or, as shown in FIG. 14 (B), the secondary battery 913 shown in FIGS. 12 (A) and 12 (B).
The sensor 921 may be provided in the. The sensor 921 is electrically connected to the terminal 911 via the terminal 922. The sensor 921 may be provided on the back side of the label 910. The same parts as those of the power storage system shown in FIGS. 12 (A) and 12 (B) are shown in FIG. 12 (A).
) And the description of the power storage system shown in FIG. 12 (B) can be appropriately referred to.

The sensor 921 includes, for example, force, displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, voice, time, hardness, electric field, current, voltage, power, and radiation. , Flow rate, humidity, gradient, vibration, odor or infrared can be measured. By providing the sensor 921, for example, data (temperature or the like) indicating the environment in which the power storage system is placed can be detected and stored in the memory in the circuit 912.

An electrode according to one aspect of the present invention is used in the secondary battery and the power storage system shown in the present embodiment. Therefore, the capacity of the secondary battery or the power storage system can be increased. In addition, the energy density can be increased. In addition, reliability can be improved. In addition, the life can be extended.

This embodiment can be implemented in combination with other embodiments as appropriate.

(Embodiment 6)
The secondary battery according to one aspect of the present invention can be used as a power source for various electric devices driven by electric power.

Specific examples of the electric device using the secondary battery according to one aspect of the present invention include a television, a display device such as a monitor, a lighting device, a desktop or notebook personal computer, a word processor, a DVD (Digital Versaille Disc), and the like. Image playback devices, portable CD players, radios, tape recorders, headphone stereos, stereos, table clocks, wall clocks, cordless telephone handsets, transceivers, portable radios, mobile phones, etc. Car phones, mobile game machines, computers,
Mobile information terminals, electronic notebooks, electronic books, electronic translators, voice input devices, video cameras, digital still cameras, toys, electric shavers, high-frequency heating devices such as microwave ovens, electric rice cookers, electric washing machines, electric vacuum cleaners, Air conditioners such as water heaters, electric fans, hair dryers, air conditioners, humidifiers, dehumidifiers, dishwashers, dish dryers, clothes dryers, duvet dryers, electric refrigerators,
Examples thereof include electric freezers, electric refrigerators and freezers, freezers for storing DNA, flashlights, electric tools such as chainsaws, smoke detectors, medical devices such as dialysis machines, and the like. Further examples include industrial equipment such as guide lights, traffic lights, conveyor belts, elevators, escalator, industrial robots, power storage systems, power leveling and power storage devices for smart grids. In addition, moving objects propelled by electric motors using electric power from secondary batteries are also included in the category of electrical equipment. Examples of the moving body include an electric vehicle (EV), a hybrid electric vehicle (HEV) having both an internal combustion engine and an electric motor, a plug-in hybrid electric vehicle (PHEV), a tracked vehicle in which these tire wheels are changed to an infinite track, and an electric assist. Examples include motorized bicycles including bicycles, motorcycles, electric wheelchairs, golf carts, small or large vessels, submarines, helicopters, aircraft, rockets, artificial satellites, space explorers and planetary explorers, and spacecraft.

The electric device can use the secondary battery according to one aspect of the present invention as a main power source for covering almost all of the power consumption. Alternatively, the electric device is a secondary power supply according to one aspect of the present invention as an uninterruptible power supply capable of supplying electric power to the electric device when the supply of electric power from the main power source or the commercial power source is stopped. Batteries can be used. Alternatively, the electric device according to one aspect of the present invention is used as an auxiliary power source for supplying electric power to the electric device in parallel with the supply of electric power from the main power source or the commercial power source to the electric device. The next battery can be used.

FIG. 15 shows a specific configuration of the electric device. In FIG. 15, the display device 700 is an example of an electric device using the secondary battery 704 according to one aspect of the present invention. Specifically, the display device 700 corresponds to a display device for receiving TV broadcasts, and includes a housing 701, a display unit 702, a speaker unit 703, a secondary battery 704, and the like. The secondary battery 704 according to one aspect of the present invention has a housing 70.
It is provided inside 1. The display device 700 can be supplied with electric power from a commercial power source, or can use the electric power stored in the secondary battery 704. Therefore, even when the power cannot be supplied from the commercial power source due to a power failure or the like, the secondary battery 70 according to one aspect of the present invention.
By using 4 as an uninterruptible power supply, the display device 700 can be used.

The display unit 702 includes a liquid crystal display device, a light emitting device having a light emitting element such as an organic EL element in each pixel, an electrophoresis display device, and a DMD (Digital Micromirror Device).
e), PDP (Plasma Display Panel), FED (Field E)
A semiconductor display device such as a mission Display) can be used.

The display device includes all information display devices such as those for receiving TV broadcasts, those for personal computers, and those for displaying advertisements.

In FIG. 15, the stationary lighting device 710 is a secondary battery 713 according to an aspect of the present invention.
It is an example of an electric device using. Specifically, the lighting device 710 includes a housing 711 and a light source 712.
, Secondary battery 713 and the like. In FIG. 15, the secondary battery 713 is the housing 711 and the light source 71.
Although the case where the secondary battery 713 is provided inside the ceiling 714 on which the 2 is installed is illustrated, the secondary battery 713 may be provided inside the housing 711. The lighting device 710 can be supplied with electric power from a commercial power source, or can use the electric power stored in the secondary battery 713. Therefore, even when the power cannot be supplied from the commercial power supply due to a power failure or the like, the lighting device 710 can be used by using the secondary battery 713 according to one aspect of the present invention as an uninterruptible power supply.

Although FIG. 15 illustrates the stationary lighting device 710 provided on the ceiling 714, the secondary battery according to one aspect of the present invention includes, for example, a side wall 715, a floor 716, a window 717, etc., other than the ceiling 714. It can be used for a stationary lighting device provided in the above, or it can be used for a tabletop lighting device or the like.

Further, as the light source 712, an artificial light source that artificially obtains light by using electric power can be used. Specifically, an incandescent lamp, a discharge lamp such as a fluorescent lamp, and a light emitting element such as an LED or an organic EL element can be mentioned as an example of the artificial light source.

In FIG. 15, the air conditioner having the indoor unit 720 and the outdoor unit 724 is an example of an electric device using the secondary battery 723 according to one aspect of the present invention. Specifically, the indoor unit 720
Has a housing 721, an air outlet 722, a secondary battery 723, and the like. In FIG. 15, the secondary battery 72
Although the case where 3 is provided in the indoor unit 720 is illustrated, the secondary battery 723 is the outdoor unit 7.
It may be provided in 24. Alternatively, a secondary battery 723 may be provided in both the indoor unit 720 and the outdoor unit 724. The air conditioner can be supplied with electric power from a commercial power source, or can use the electric power stored in the secondary battery 723. In particular, when the secondary battery 723 is provided in both the indoor unit 720 and the outdoor unit 724, the secondary battery 723 according to one aspect of the present invention is provided even when the power cannot be supplied from the commercial power source due to a power failure or the like.
The air conditioner can be used by using the as an uninterruptible power supply.

Although FIG. 15 illustrates a separate type air conditioner composed of an indoor unit and an outdoor unit, it is an integrated air conditioner battery having the functions of an indoor unit and an outdoor unit in one housing. A secondary battery according to one aspect of the present invention can also be used as the shoulder.

In FIG. 15, the electric refrigerator-freezer 730 is an example of an electric device using the secondary battery 734 according to one aspect of the present invention. Specifically, the electric freezer / refrigerator 730 has a housing 731, a refrigerator door 732, a freezer door 733, a secondary battery 734, and the like. In FIG. 15, the secondary battery 734 is provided inside the housing 731. The electric refrigerator-freezer 730 can be supplied with electric power from a commercial power source, or can use the electric power stored in the secondary battery 734. Therefore, even when the power cannot be supplied from the commercial power source due to a power failure or the like, the electric refrigerator-freezer 730 can be used by using the secondary battery 734 according to one aspect of the present invention as an uninterruptible power supply.

Among the above-mentioned electric devices, high-frequency heating devices such as microwave ovens and electric devices such as electric rice cookers require high electric power in a short time. Therefore, by using the secondary battery according to one aspect of the present invention as an auxiliary power source for assisting the electric power that cannot be covered by the commercial power source, it is possible to prevent the breaker of the commercial power source from being tripped when the electric device is used. ..

Also, during times when electrical equipment is not used, especially during times when the ratio of the amount of power actually used (called the power usage rate) to the total amount of power that can be supplied by the commercial power supply source is low. By storing power in the next battery, it is possible to suppress an increase in the power usage rate outside the above time zone. For example, in the case of the electric refrigerator / freezer 730, the temperature is low, and the refrigerator door 732,
Electric power is stored in the secondary battery 734 at night when the freezing room door 733 is not opened and closed. By using the secondary battery 734 as an auxiliary power source in the daytime when the temperature rises and the refrigerating room door 732 and the freezing room door 733 are opened and closed, the daytime power usage rate can be kept low.

This embodiment can be implemented in combination with other embodiments as appropriate.

(Embodiment 7)
Next, a mobile information terminal, which is an example of an electric device, will be described with reference to FIG.

16 (A) and 16 (B) show a tablet terminal 800 that can be folded in half. FIG. 16
(A) is an open state, and the tablet terminal 800 has a housing 801 and a display unit 802a.
It has a display unit 802b, a display mode changeover switch 803, a power supply switch 804, a power saving mode changeover switch 805, and an operation switch 807.

A part of the display unit 802a can be a touch panel area 808a, and data can be input by touching the displayed operation key 809. The display unit 802a shows, for example, a configuration in which half of the area has a display-only function and the other half of the area has a touch panel function, but the configuration is not limited to this. The entire area of the display unit 802a may have a touch panel function. For example, the entire surface of the display unit 802a can be displayed as a keyboard button to form a touch panel, and the display unit 802b can be used as a display screen.

Further, in the display unit 802b as well, a part of the display unit 802b can be a touch panel area 808b as in the display unit 802a. Further, by touching the position where the keyboard display switching button 810 of the touch panel is displayed with a finger or a stylus, the display unit 80
A keyboard button can be displayed on 2b.

Further, touch input can be simultaneously performed on the touch panel area 808a and the touch panel area 808b.

Further, the display mode changeover switch 803 can switch the display direction such as vertical display or horizontal display, and can select switching between black-and-white display and color display. The power saving mode changeover switch 805 can optimize the brightness of the display according to the amount of external light during use detected by the optical sensor built in the tablet terminal. The tablet-type terminal may incorporate not only an optical sensor but also other detection devices such as a gyro, an acceleration sensor, and other sensors that detect tilt.

Further, FIG. 16A shows an example in which the display areas of the display unit 802b and the display unit 802a are the same, but the display area is not particularly limited, and one size and the other size may be different, and the display quality is also good. It may be different. For example, one may be a display panel capable of displaying a higher definition than the other.

FIG. 16B shows a closed state, and the tablet terminal 800 has a housing 801, a solar cell 811, a charge / discharge control circuit 850, a battery 851, and a DCDC converter 852. In FIG. 16B, the battery 851 and DCD are examples of the charge / discharge control circuit 850.
The configuration having the C converter 852 is shown, and the battery 851 has the secondary battery described in the above embodiment.

Since the tablet terminal 800 can be folded in half, the housing 801 can be closed when not in use. Therefore, since the display unit 802a and the display unit 802b can be protected, it is possible to provide the tablet type terminal 800 having excellent durability and reliability from the viewpoint of long-term use.

In addition to this, the tablet-type terminals shown in FIGS. 16A and 16B have a function of displaying various information (still images, moving images, text images, etc.), a calendar, a date, a time, and the like. It can have a function of displaying on a display unit, a touch input function of performing a touch input operation or editing information displayed on the display unit, a function of controlling processing by various software (programs), and the like.

The solar cell 811 mounted on the surface of the tablet terminal can supply electric power to the touch panel, the display unit, the video signal processing unit, or the like. The solar cell 811 can be provided on one side or both sides of the housing 801 and is suitable because it can be configured to efficiently charge the battery 851. As the battery 851, if the secondary battery according to one aspect of the present invention is used, there is an advantage that the size can be reduced.

Further, the configuration and operation of the charge / discharge control circuit 850 shown in FIG. 16 (B) are shown in FIG. 16 (C).
A block diagram will be shown and explained in. In FIG. 16C, the solar cell 811 and the battery 851 are shown.
DCDC converter 852, converter 853, switches SW1 to SW3, display unit 80
2 is shown, battery 851, DCDC converter 852, converter 85.
3. The switches SW1 to SW3 correspond to the charge / discharge control circuit 850 shown in FIG. 16B.

First, an example of operation when power is generated by the solar cell 811 by external light will be described.
The power generated by the solar cell is DCDC so that it becomes the voltage for charging the battery 851.
The converter 852 steps up or down. Then, when the power from the solar cell 811 is used for the operation of the display unit 802, the switch SW1 is turned on, and the converter 853 steps up or down the voltage required for the display unit 802. Further, when the display is not performed on the display unit 802, the SW1 may be turned off and the SW2 may be turned on to charge the battery 851.

The solar cell 811 is shown as an example of the power generation means, but is not particularly limited, and the battery 851 is charged by another power generation means such as a piezoelectric element (piezo element) or a thermoelectric conversion element (Peltier element). May be. For example, a non-contact power transmission module that wirelessly (non-contactly) transmits and receives power for charging may be used, or a configuration may be performed in combination with other charging means.

Further, it goes without saying that the electric device shown in FIG. 16 is not particularly limited as long as the secondary battery described in the above embodiment is provided.

(Embodiment 8)
Further, an example of a moving body, which is an example of an electric device, will be described with reference to FIG.

The secondary battery described in the previous embodiment can be used as the control battery. The control battery can be charged by external power supply using plug-in technology or contactless power supply. If the moving body is an electric vehicle for railways, it can be charged by supplying electric power from an overhead wire or a conductive rail.

17 (A) and 17 (B) show an example of an electric vehicle. The electric vehicle 860 is equipped with a battery 861. The power of the battery 861 is adjusted in output by the control circuit 862 and supplied to the drive device 863. The control circuit 862 includes a ROM (not shown).
It is controlled by a processing device 864 having a RAM, a CPU, and the like.

The drive device 863 is composed of a DC motor or an AC motor alone, or a combination of a motor and an internal combustion engine. The processing device 864 is based on input information of the driver's operation information (acceleration, deceleration, stop, etc.) of the electric vehicle 860 and information during traveling (information such as uphill and downhill, load information on the drive wheels, etc.). , The control signal is output to the control circuit 862. The control circuit 862
The control signal of the processing device 864 adjusts the electric energy supplied from the battery 861 to control the output of the drive device 863. If an AC motor is installed, an inverter that converts direct current to alternating current is also built-in, although not shown.

The battery 861 can be charged by external power supply by plug-in technology. For example, the battery 861 is charged from a commercial power source through a power plug. Charging is
It can be converted into a DC constant voltage having a constant voltage value via a conversion device such as an AC / DC converter. By mounting the secondary battery according to one aspect of the present invention as the battery 861, it is possible to contribute to increasing the capacity of the battery and to improve the convenience. Further, if the battery 861 itself can be made smaller and lighter by improving the characteristics of the battery 861, it contributes to the weight reduction of the vehicle, so that the fuel efficiency can be improved.

Needless to say, the secondary battery of one aspect of the present invention is not particularly limited to the electronic devices shown above.

This embodiment can be implemented in combination with other embodiments as appropriate.

(Embodiment 9)
In this embodiment, an example of mounting a flexible secondary battery in an electronic device will be described.

FIG. 18 shows an example of mounting the flexible secondary battery shown in the third embodiment on an electronic device. Electronic devices to which a power storage device with a flexible shape is applied include, for example, television devices (also referred to as televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones. (Also referred to as a mobile phone or a mobile phone device), a portable game machine, a mobile information terminal, a sound reproduction device, a large game machine such as a pachinko machine, and the like can be mentioned.

It is also possible to incorporate a power storage device having a flexible shape along the inner or outer wall of a house or building, or along the curved surface of the interior or exterior of an automobile.

FIG. 18A shows an example of a mobile phone. The mobile phone 7400 has a housing 7401.
In addition to the display unit 7402 built into the unit, it is equipped with an operation button 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like. The mobile phone 7400 has a power storage device 7407.

FIG. 18B shows a state in which the mobile phone 7400 is curved. Mobile phone 740
When 0 is deformed by an external force to bend the whole, the power storage device 7407 provided inside the zero is also bent. Further, at that time, the state of the bent power storage device 7407 is shown in FIG. 18 (C).
). The power storage device 7407 is a thin secondary battery. The power storage device 7407 is fixed in a bent state. The power storage device 7407 has a lead electrode 7408 electrically connected to the current collector 7409. For example, the current collector 7409 is a copper foil, which is partially alloyed with gallium to improve the adhesion to the active material layer in contact with the current collector 7409, and the power storage device 7407.
It has a highly reliable configuration in the bent state.

FIG. 18D shows an example of a bangle type display device. The portable display device 7100 is
It includes a housing 7101, a display unit 7102, an operation button 7103, and a power storage device 7104.
Further, FIG. 18 (E) shows the state of the electricity storage device 7104 bent. When the power storage device 7104 is attached to the user's arm in a bent state, the housing is deformed and the curvature of a part or the whole of the power storage device 7104 changes. The radius of curvature is the value of the radius of the circle corresponding to the degree of bending at any point on the curve, and the reciprocal of the radius of curvature is called the curvature. Specifically, a part or all of the main surface of the housing or the power storage device 7104 changes within the range of the radius of curvature of 40 mm or more and 150 mm or less. The radius of curvature on the main surface of the power storage device 7104 is 40 mm or more and 150.
High reliability can be maintained if the range is mm or less.

FIG. 18F shows an example of a wristwatch-type personal digital assistant. The mobile information terminal 7200 includes a housing 7201, a display unit 7202, a band 7203, a buckle 7204, and an operation button 72.
05, input / output terminal 7206 and the like are provided.

The personal digital assistant 7200 can execute various applications such as mobile phone, e-mail, text viewing and creation, music playback, Internet communication, and computer games.

The display unit 7202 is provided with a curved display surface, and can display along the curved display surface. Further, the display unit 7202 is provided with a touch sensor and can be operated by touching the screen with a finger or a stylus. For example, the icon 72 displayed on the display unit 7202.
You can start the application by touching 07.

In addition to setting the time, the operation button 7205 can have various functions such as power on / off operation, wireless communication on / off operation, manner mode execution / cancellation, and power saving mode execution / cancellation. .. For example, the function of the operation button 7205 can be freely set by the operation system built in the mobile information terminal 7200.

Further, the mobile information terminal 7200 can execute short-range wireless communication standardized for communication. For example, by communicating with a headset capable of wireless communication, it is possible to make a hands-free call.

Further, the mobile information terminal 7200 is provided with an input / output terminal 7206, and data can be directly exchanged with another information terminal via a connector. It is also possible to charge via the input / output terminal 7206. The charging operation may be performed by wireless power supply without going through the input / output terminal 7206.

The display unit 7202 of the portable information terminal 7200 has a power storage device including the electrode member of one aspect of the present invention. For example, the power storage device 7104 shown in FIG. 18E can be incorporated in a curved state inside the housing 7201 or in a bendable state inside the band 7203.

FIG. 18G shows an example of an armband-shaped display device. The display device 7300 is a display unit 7.
It has 304 and has a power storage device of one aspect of the present invention. Further, the display device 7300 can be provided with a touch sensor in the display unit 7304, and can also function as a portable information terminal.

The display surface of the display unit 7304 is curved, and display can be performed along the curved display surface. Further, the display device 7300 can change the display status by communication standard short-range wireless communication or the like.

Further, the display device 7300 is provided with an input / output terminal, and can directly exchange data with another information terminal via a connector. It can also be charged via the input / output terminals.
The charging operation may be performed by wireless power supply without going through the input / output terminals.

This embodiment can be implemented in combination with other embodiments as appropriate.

Hereinafter, one aspect of the present invention will be specifically described with reference to examples.
<Synthesis of graphene oxide>
First, graphene oxide was synthesized by the following method. First, 4 g of graphite (manufactured by Chuetsu Graphite Industry Co., Ltd., BF-40AK) and 138 mL of concentrated sulfuric acid (manufactured by Kanto Chemical Co., Inc., 96%) were mixed. Next, 18 g of potassium permanganate (manufactured by Kishida Chemical Co., Ltd., 99%) was added while stirring in an ice bath. Further, the ice bath was removed and the mixture was stirred at 25 ° C. for 2.5 hours to obtain a mixed solution.

Next, the obtained mixture was slowly added with 276 mL of pure water while stirring in an ice bath to dilute it. Next, the mixture was stirred and reacted in an oil bath at about 95 ° C. for 15 minutes, diluted with 400 mL of pure water, and further diluted with 54 mL of hydrogen peroxide solution (manufactured by Mitsubishi Gas Chemical Company, Inc., concentration 31 wt%).
Was added to inactivate unreacted potassium permanganate to obtain a mixed solution. The roughness of the eyes is 0.45
The mixed solution obtained with a μm membrane filter was suction-filtered to collect the precipitate.

After washing the obtained precipitate with 3.5% hydrochloric acid (Wako Pure Chemical Industries, Ltd.), the precipitate is approximately 5
After adding 500 mL of pure water per g, the mixture was centrifuged to collect the precipitate multiple times, and the graphene oxide, which was the precipitate, was washed. Then, it was evaporated and dried to obtain graphene oxide. This is referred to as GO1-6.

Similar to GO1-6, 12 g of potassium permanganate was reacted with 4 g of raw material graphite in 138 mL of concentrated sulfuric acid at 25 ° C. for 4.5 hours, diluted and then deactivated with 36 mL of hydrogen peroxide solution to obtain graphene oxide. Is GO2-6.

Similar to GO1-6, 8 g of potassium permanganate was reacted with 4 g of raw material graphite in 138 mL of concentrated sulfuric acid at 25 ° C. for 4.5 hours, diluted and then deactivated with 24 mL of hydrogen peroxide solution to obtain graphene oxide. Is GO3-6.

Similar to GO1-6, 12 g of potassium permanganate was reacted with 2 g of raw material graphite in 92 mL of concentrated sulfuric acid at 25 ° C for 2 hours and 35 ° C for 0.5 hours, and after dilution, hydrogen peroxide solution 3 was used.
The graphene oxide obtained by deactivating with 6 mL is referred to as GO4-6.

<XPS>
The above graphene oxide is subjected to X-ray photoelectron spectroscopy (XPS: X-ray Photoelectron).
It was measured by tron spectroscopy). The measurement was performed using monochromatic light Al (1486.6 eV) as an X-ray source with a measurement area of 100 μm and a take-out angle of 45 °. Table 1 shows the element ratios of the measurement results, and Table 2 shows the analysis results of the bond state. It should be noted that graphene oxide contains H but is not detected by XPS. The composition error is ±
It is about 1 atm%.

In Table 1, C / O is simply a numerical value of the element ratio of C and O. For example, GO3-
In No. 6, the C / O is 3.4 to 3.8 when the error is included, but the values are not taken into consideration. Table 2 is based on the results of waveform separation analysis, and the error is usually about ± 3%, but C =
Since the chemical shift of the peak of C is small, the error is large.

In GO3-6, the composition ratio C / O was clearly different from other conditions. Further, it can be seen that 10% or more of sp2 bonds are detected from the bound state, and many unreacted sites remain.

<Titration>
The results of investigating the reaction amount of the oxidizing agent KMnO ₄ (Mn _{2O 7} under concentrated sulfuric acid) in the above reaction are shown below. That is, the solution being reacted was dropped onto a large amount of pure water, and the obtained supernatant was colorimetrically titrated using hydrogen peroxide solution. The reaction conditions were fixed at 4 g of graphite, 138 mL of concentrated sulfuric acid, and a temperature of 25 ° C., and the amount of potassium permanganate was 8 g, 10 g, 12 g, 15 g, and 18 g.
I shook the condition. The relationship between the amount of potassium permanganate consumed per weight of the substrate graphite and the reaction time is shown in FIG. The measurement points shown in white in the figure indicate that potassium permanganate could not be detected. In the system of 18 g of oxidizing agent, potassium permanganate was detected at all the measuring points.

In FIG. 19, although the oxidant concentration has changed, no change has been observed in the oxidant consumption rate, and it is considered that the reaction rate depends on graphite. When potassium permanganate is 15 g or less with respect to 4 g of graphite, the reaction time is 4.5 hours and potassium permanganate (Mn ₂ O ₇ in the reaction solution) is contained in the solution.
) Was not detected. In addition, since the precipitate is removed at the time of titration, in graphite,
Alternatively, note that no oxidant bound to graphite is detected.

<FT-IR>
Next, it was analyzed by infrared absorption spectroscopy (FT-IR). That is, a single reflection ATR method (prism:
The graphene oxide film was measured with Ge).

Similar to GO1-6, 18 g of potassium permanganate was reacted with 4 g of raw material graphite in 138 mL of concentrated sulfuric acid at 25 ° C. for 4.5 hours, diluted and then deactivated with 54 mL of hydrogen peroxide solution to obtain graphene oxide. Is GO1-6a. Further, 1-methyl-2-pyrrolidone (NMP) was added to GO1-6a, and the slurry that was kneaded and dispersed was coated on a polyimide film (Kapton (registered trademark) H type) by a blade method and dried. It is GO1-7.

NMP is added to GO3-6, and the slurry that has been kneaded and dispersed is coated on a polyimide film by a blade method, and the dried film is designated as GO3-7.

25 g of potassium permanganate in 138 mL of concentrated sulfuric acid for 4 g of raw material graphite
The graphene oxide obtained by reacting at ° C. for 4.5 hours and deactivating with 54 mL of hydrogen peroxide solution after dilution is designated as GO5-6. Further, NMP is added to GO5-6, and the slurry which has been kneaded and dispersed is coated on a polyimide film by a blade method, and the dried film is designated as GO5-7.

25 g of potassium permanganate in 138 mL of concentrated sulfuric acid for 4 g of raw material graphite
The graphene oxide obtained by reacting at ° C. for 24 hours and deactivating with 63 mL of hydrogen peroxide solution after dilution is designated as GO6-6. Further, NMP is added to GO6-6, and the slurry which has been kneaded and dispersed is coated on a polyimide film by a blade method, and the dried film is referred to as GO6-7.

FIG. 20 shows the results of baseline correction analysis of the above FT-IR measurement results of GO1-7, GO3-7, GO5-7, and GO6-7. GO3-7, which was suggested by XPS to have a clear unoxidized site, had a wide and gentle peak in the range of 3000 to 1300 cm ^-1 , and the spectrum was suspected to have a scattering component. 6-7, which had consumed all of the potassium permanganate in the solution when diluted and stirred at 95 ° C for 15 minutes, did not have a peak at 1570 cm ^-1 , and was stirred at 95 ° C for 15 minutes in the presence of potassium permanganate. GO1-7 and GO5-7 were 157
The result was that it had a peak at 0 cm ^-1 .

<Measurement of resistivity>
Graphene oxide was reduced by heating the above GO1-6 under vacuum at 170 ° C. for 10 hours. Further, the obtained sample was packed in a pellet die having a diameter of 5 mm, pressurized with a hydraulic pump for 10 minutes, released, and then pressed again for 10 minutes to prepare RGO pellets 1-8. At this time, the pressure per unit area applied to the powder was about 7.5 Mgf / cm ² . Similarly, GO2-6 to R
GO pellets 2-8, GO3-6 to RGO pellets 3-8, GO5-6 to RGO
Pellets 5-8 were made.

Obtained RGO pellets 1-8, RGO pellets 2-8, RGO pellets 3-8, RGO
The specific resistance of pellets 5-9 was measured by the DC four-terminal van der Pauw method.
A Resist8300 (manufactured by Toyo Corporation) was used for the resistivity measurement.

Table 3 shows the measurement results of resistivity.

Under the same reduction conditions, there was a large difference in the resistivity of the obtained graphene (RGO). That is, the resistivity was clearly low in the RGO pellets 3-9 in which the unoxidized portion was left. It is known that the conductivity of graphene has a strong correlation with the proportion of sp2 bonds due to C = C of the constituent carbon (C), and that the greater the proportion of sp2 bonds due to C = C, the higher the conductivity tends to be. There is. The results were correlated with the XPS analysis results and the FT-IR analysis. From these GO3
It can be said that -6 is graphene oxide in which graphene having high electrical conductivity can be easily obtained.

(Dispersity evaluation)
If a large amount of unoxidized sites are left, peeling and dispersion in a solvent may be deteriorated, which is a cause for concern. In order to evaluate these, the battery characteristics were evaluated using the conductive auxiliary agent of the secondary battery.

The synthesis conditions of the graphene oxide sample newly synthesized for battery characteristic evaluation are described.
Similar to GO5-6, 18 g of potassium permanganate is added to 4 g of raw material graphite and 1 of concentrated sulfuric acid.
The graphene oxide obtained by reacting in 38 mL at 25 ° C. for 4.5 hours and deactivating with 54 mL of hydrogen peroxide solution after dilution is designated as GO5-6a. Further, the graphene oxide obtained by reacting 4 g of raw material graphite with 15 g of potassium permanganate in 138 mL of concentrated sulfuric acid at 25 ° C. for 4.5 hours and deactivating with 45 mL of hydrogen peroxide solution after dilution was referred to as GO6-6. do. 10 g of potassium permanganate was reacted with 4 g of raw material graphite in 138 mL of concentrated sulfuric acid at 25 ° C. for 4.5 hours, diluted and then deactivated with 30 mL of hydrogen peroxide solution to obtain graphene oxide.
It is set to 6. That is, GO5-6a, GO6-6, GO2-6, GO7-6, and GO3-6 are synthetic conditions in which only the amount of potassium permanganate and the proportional amount of hydrogen peroxide solution of the deactivating agent are changed.

(Making a secondary battery)
A method for manufacturing a secondary battery will be described. First, graphene oxide was added to LiFePO ₄ which was not coated with carbon and was prepared by the solid phase method, and NMP was added as a solvent and kneaded. Kneading refers to kneading with high viscosity, and is one of the methods for easily loosening the aggregation of graphene oxide and active substances. Next, an NMP solution of PVdF (# 7300 manufactured by Kureha Corporation) was added as a binder to the mixture of graphene oxide and LiFePO ₄ , and then NMP was further added as a polar solvent and kneaded to prepare a slurry. The slurry prepared by the above method was applied onto the current collector and dried at 80 ° C. for 40 minutes in an air atmosphere to prepare an electrode having an active material layer formed on the current collector. The current collector has a film thickness of 20 μm.
The aluminum of m coated with carbon black by about 1 μm was used. Also, Li
FePO ₄ has a specific surface area of ca. The crystallite size was 11 m ² / g and the crystallite size was 110 nm. The ratio of the electrode layers was set to LiFePO ₄ : GO: PVdF = 93: 2: 5 in terms of weight ratio. Here, when LiFePO ₄ is not carbon-coated, its electrical conductivity is poor and its capacity is considerably difficult to obtain, but it is known that when graphene oxide coated with dispersion is used, the capacity can be increased by adding a small amount. In other words, it can be said that dispersibility can be evaluated because the volume is difficult to obtain with graphene oxide that is not so peeled off or graphene oxide that is difficult to disperse in the active material.

Further, the graphene oxide in the electrode was reduced by heating at 170 ° C. for 10 hours in a vacuum atmosphere.
Pressing was performed so that the electrode density was about 2.0 g / cm ² . The positive electrode is punched to a diameter of 12 mm, lithium metal is used as the counter electrode, and the electrolytic solution is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) and lithium hexafluorophosphate (Li).
A solution of PF ₆ ) (concentration 1M) is used, and the separator is porous polypropylene (PP).
) Was used to manufacture a 2032 type coin battery. EC / DE including 1M LiPF ₆
Code LBG-96533 manufactured by Kishida Chemical Co., Ltd. was used as the C solution.

From GO5-6a to the positive electrode 5-9 and the battery 5a using the same, GO6-6 to the positive electrode 6-9 and the battery 6-a, and GO2-6 to the positive electrode 2-9 and 2-a. , The positive electrode 7-9 and the battery 7-a were obtained from GO7-6, and the positive electrode 3-9 and the battery 3-a were obtained from GO3-6. The amount of active material supported by the positive electrode 6-9, the positive electrode 2-9, the positive electrode 7-9, and the positive electrode 3-9 is 6.5 to 7.0.
It was mg / cm ² .

Further, using the same active material, an electrode was similarly produced using graphene (manufactured by Cheap Tubes) by a direct peeling method having good conductivity but weak interaction with the active material and poor dispersibility. The blending ratio was set to LiFePO ₄ : graphene: PVdF = 90: 5: 5 by weight. A positive electrode and a battery were manufactured in the same manner as described above. The obtained positive electrode is referred to as a positive electrode G, and the battery is referred to as a battery G. The amount of active material supported by the positive electrode G was 6.0 mg / cm ² . Further, an electrode was produced using acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., Denka Black (registered trademark), abbreviated as AB). The compounding ratio is LiFePO ₄ : AB: PVdF = 80: by weight.
It was set to 15: 5. A positive electrode and a battery were manufactured in the same manner as described above. The obtained positive electrode is referred to as a positive electrode AB, and the battery is referred to as a battery AB.

(Battery capacity measurement)
The discharge capacity of the obtained battery was measured. Charging was performed by applying CCCV, that is, at a constant current of 0.2 C until it became 4.3 V, and then holding it at a constant voltage of 4.3 V until the current value became 0.05 C. Discharge was performed by applying CC, that is, a constant current of 1 C until the voltage reached 2.0 V. The discharge curve at 1C is shown in FIGS. 21 (A) and 21 (B). 21 (B) shows the battery 5- in FIG. 21 (A).
It is a figure which enlarged and showed the vertical axis and the horizontal axis of the measured value of a, battery 6-a, battery 2-a, battery 7-a and battery 3-a.

In FIG. 21B, the battery 3-a showed the same capacity as the others. In addition, the discharge potential PLATEau
There is no big difference in the point where it starts to deviate from the (flat part), and the discharge potential is rather higher than the others. Here, it is considered that the dispersibility is related to the easiness of disengagement from PLATEau (the susceptibility of polarization), and the discharge potential is related to the resistance (connection degree and electrical conductivity) of the conductive path of the conductive auxiliary agent. Therefore, it was suggested from FIG. 21 (B) that GO3-9, which leaves an unoxidized site, has a dispersibility without any particular problem.

On the other hand, from FIG. 21 (A), it was found that the battery G using graphene has sufficiently high electrical conductivity, but is easily detached from PLATEau from the initial stage. The cause is poor dispersibility in active materials.

As described above, it was shown that graphene oxide has both sufficient exfoliation and dispersibility and easy formation of graphene having high electrical conductivity.

200 Positive Electrode 201 Positive Electrode Collector 202 Positive Electrode Active Material Layer 300 Secondary Battery 301 Positive Electrode Can 302 Negative Electrode Can 303 Gasel 304 Positive Electrode 305 Positive Electrode Collector 306 Positive Electrode Active Material Layer 307 Negative Electrode 308 Negative Electrode Collector 309 Negative Electrode Active Material Layer 310 Separator 401 Container 402 Graphene oxide dispersion 403 Object 404 Conductor 405 Container 406 Electrolyte 407 Conductor 408 Counter electrode 500 Secondary battery 501 Positive electrode current collector 502 Positive electrode active material layer 503 Positive electrode 504 Negative electrode current collector 505 Negative electrode active material layer 506 Negative electrode 507 Separator 508 Electrode 509 Exterior 510 Positive electrode lead electrode 511 Negative electrode lead electrode 512 Welding area 513 Curved part 600 Secondary battery 601 Positive electrode cap 602 Battery can 603 Positive electrode terminal 604 Positive electrode 605 Separator 606 Negative electrode 607 Negative electrode terminal 608 Insulation plate 609 Insulation plate 610 gasket (insulation packing)
611 PTC element 612 Safety valve mechanism 700 Display device 701 Housing 702 Display unit 703 Speaker unit 704 Secondary battery 710 Lighting device 711 Housing 712 Light source 713 Secondary battery 714 Ceiling 715 Side wall 716 Floor 717 Window 720 Indoor unit 721 Housing 722 Blower Mouth 723 Rechargeable battery 724 Outdoor unit 730 Electric refrigerator / freezer 731 Housing 732 Refrigerating room door 733 Freezing room door 734 Secondary battery 800 Tablet type terminal 801 Housing 802 Display unit 802a Display unit 802b Display unit 803 Display mode changeover switch 804 Power switch 805 Power saving mode changeover switch 807 Operation switch 808a Area 808b Area 809 Operation key 810 Keyboard display changeover button 81 Solar battery 850 Charge / discharge control circuit 851 Battery 852 DCDC converter 853 Converter 860 Electric vehicle 861 Battery 862 Control circuit 863 Drive unit 864 processing device 900 circuit board 910 label 911 terminal 912 circuit 913 secondary battery 914 antenna 915 antenna 916 layer 917 layer 918 antenna 919 terminal 920 display device 921 sensor 922 terminal 951 terminal 952 terminal 981 film 982 film 990 secondary battery 991 exterior 994 Negative 995 Positive 996 Separator 997 Lead electrode 998 Lead electrode 1700 Curved surface 1701 Flat surface 1702 Curve 1703 Curved radius 1704 Curvature center 1800 Curvature center 1801 Film 1802 Curvature radius 1803 Film 1804 Curved radius 7100 Portable display device 7101 Housing 7102 Display unit 7103 Operation button 7104 Power storage device 7200 Mobile information terminal 7201 Housing 7202 Display unit 7203 Band 7204 Buckle 7205 Operation button 7206 Input / output terminal 7207 Icon 7300 Display device 7304 Display unit 7400 Mobile phone 7401 Housing 7402 Display unit 7403 Operation button 7404 External connection port 7405 Speaker 7406 Mike 7407 Power storage device 7408 Lead electrode 7409 Current collector

Claims (3)

Graphene oxide having a carbon atom to oxygen atom ratio (C / O) of 2.5 or more and 4 or less in X-ray photoelectron spectroscopy. In claim 1, graphene oxide having a carbon atom to oxygen atom ratio (C / O) of 3 or more and 4 or less. The graphene oxide according to claim 1 or 2, wherein the ratio (C / O) of a carbon atom to an oxygen atom is 3 or more and 3.7 or less.

Images