JP2002110233A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Problem] To provide a non-aqueous electrolyte secondary battery in which the problem of swelling due to gas generation in a container having a wall thickness of 0.25 mm or less is solved and the charge / discharge cycle characteristics are excellent. Aim. SOLUTION: A container 1, a positive electrode 6 contained in the container, a negative electrode 9 contained in the container 1 and containing a negative electrode active material, and a non-aqueous electrolyte contained in the container 1 In the non-aqueous electrolyte secondary battery provided with, the thickness X of the wall of the container 1 is 0.25 mm or less, and the negative electrode active material is:
The abundance ratio of particles having a particle diameter of 5 μm or less is 5% by volume or less, and the BET specific surface area by N ₂ adsorption is ² to 50 m ² /
g of the nonaqueous electrolyte, wherein the nonaqueous electrolyte contains a nonaqueous solvent having a viscosity of 4 cP or more at 20 ° C. in which the electrolyte is dissolved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art As a non-aqueous electrolyte secondary battery for portable equipment such as a portable telephone, a lithium ion secondary battery has been commercialized. As this lithium ion secondary battery,
An electrode group having a separator interposed between a positive electrode containing an active material such as lithium cobalt oxide (LiCoO ₂ ) and a negative electrode containing a carbon-based material such as a graphitized material or a carbonaceous material together with a nonaqueous electrolytic solution in a metal can There is known a configuration in which it is housed inside. In the non-aqueous electrolyte, a low-viscosity, low-boiling non-aqueous electrolyte as described in JP-A-4-14769, that is, a mixed solvent comprising propylene carbonate, ethylene carbonate, and γ-butyrolactone is used. Mainly, the ratio of γ-butyrolactone is 10% of the whole solvent.
For example, a non-aqueous electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent of about 50% by volume is used.

At present, there is a demand for lighter and thinner batteries as portable devices become thinner. For this reason, instead of a metal can, a container formed of a film material such as a laminate film is used as a container (exterior material) for storing the electrode group, or the thickness of the metal can is reduced to 0.3 mm or less. That is being considered. By forming the container from a film material, it is possible to reduce the weight of the container as compared with a metal can, and the thickness (wall thickness) of the container wall can be reduced. It is possible to reduce the thickness.

However, in a non-aqueous electrolyte secondary battery including a low-viscosity non-aqueous electrolyte having the above-described composition, although the non-aqueous electrolyte quickly permeates the negative electrode, a large amount of gas is discharged from the negative electrode during initial charge and discharge. Gas is easily generated when the positive electrode reacts with the non-aqueous electrolyte when stored at a high temperature of 60 ° C. or higher to cause oxidative decomposition of the non-aqueous electrolyte. In such a secondary battery, when a container formed using a film material is used as an exterior material, there is a problem that the container swells and deforms due to gas generation. If the container is deformed, the battery will not fit in the electronic device,
Alternatively, malfunction of the electronic device may be caused.

[0005]

Although it has been considered to use a high-viscosity non-aqueous electrolyte to suppress gas generation during initial charge and discharge and high-temperature storage, the use of such a non-aqueous electrolyte is considered. According to the secondary battery, it is difficult to obtain a sufficient cycle life.

It is an object of the present invention to provide a wall having a thickness of 0.25 mm.
An object of the present invention is to provide a non-aqueous electrolyte secondary battery that solves the following problem of swelling due to gas generation in a container and has excellent charge / discharge cycle characteristics.

[0007]

The non-aqueous electrolyte secondary battery according to the present invention comprises a container, a positive electrode housed in the container,
In a non-aqueous electrolyte secondary battery including a negative electrode contained in the container and containing a negative electrode active material and a non-aqueous electrolyte contained in the container, the thickness of the wall of the container is 0.1 mm.
25 mm or less, the negative electrode active material contains graphitized particles having an abundance ratio of particles having a particle diameter of 5 μm or less of 5% by volume or less and a BET specific surface area by N ₂ adsorption of ² to 50 m ² / g, In addition, the non-aqueous electrolyte contains a non-aqueous solvent having a viscosity of 4 cP or more at 20 ° C. and in which the electrolyte is dissolved.

A non-aqueous electrolyte secondary battery according to the present invention comprises a container, a positive electrode housed in the container, a negative electrode housed in the container and containing a negative electrode active material, and a housing housed in the container. In a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte, the thickness of the container wall is 0.25 mm or less,
The negative electrode active material contains graphitized particles satisfying the following formula (1), and the non-aqueous electrolyte has a viscosity of 4 cP or more at 20 ° C., and includes a non-aqueous solvent in which the electrolyte is dissolved. It is a feature.

0 ≦ P / S ≦ 2.5 (1) In the above (1), P is an abundance ratio (volume%) of particles having a particle diameter of 5 μm or less in the graphitized particles.
S is the BET specific surface area (m ² / g) of the graphitized particles due to N ₂ adsorption.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A non-aqueous electrolyte secondary battery according to the present invention comprises a container having a wall thickness of 0.25 mm or less, an electrode housed in the container, and a separator interposed between a positive electrode and a negative electrode. And a non-aqueous electrolyte held by the electrode group.

Hereinafter, the positive electrode, the negative electrode, the separator, the non-aqueous electrolyte and the container will be described.

1) Positive Electrode This positive electrode has a positive electrode current collector and a positive electrode layer supported on one or both surfaces of the positive electrode current collector and containing an active material and a binder.

As the positive electrode active material, various oxides,
For example, manganese dioxide, lithium manganese composite oxide,
Lithium-containing nickel oxide, lithium-containing cobalt acid
Compound, lithium-containing nickel cobalt oxide, lithium
Iron oxide, vanadium oxide containing lithium,
Chalcogen compounds such as titanium sulfide and molybdenum disulfide
And the like. Among them, lithium-containing edge
Oxide (for example, LiCoO_Two), Lithium containing
Nickel cobalt oxide (eg, LiNi_0.8Co_0.2O
_Two), Lithium manganese composite oxide (eg, LiMn)_Two
O_Four, LiMnO _Two) Can provide high voltage
Preferred.

The binder has a function of binding the positive electrode active materials and a function of binding the positive electrode active material and the positive electrode current collector. Examples of such a binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (P
VdF), an ethylene-propylene-diene copolymer (E
PDM), styrene-butadiene rubber (SBR) and the like can be used. When the positive electrode, the negative electrode, and the separator are integrated by the first and second manufacturing methods described below, it is preferable to use a thermosetting resin as the binder, and PVdF is particularly preferable.

[0015] The positive electrode layer may further contain a conductive agent. Examples of such a conductive agent include acetylene black, carbon black, and graphite.

The mixing ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder. .

The thickness of the positive electrode layer is preferably in the range of 10 to 150 μm. Here, the thickness of the positive electrode layer means a distance between the surface of the positive electrode layer facing the separator and the surface of the positive electrode layer contacting the current collector. When the positive electrode layer is supported on both surfaces of the positive electrode current collector, the thickness of one side of the positive electrode layer is set to 10 to 150 μm, and the total thickness of the positive electrode active material layer is set to 20 to 300 μm. desirable. A more preferable range of the thickness of the positive electrode layer is 30 to 100 μm. By setting the thickness of the positive electrode layer in the range of 30 to 100 μm, large current discharge characteristics and cycle life can be significantly improved.

As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used.
These conductive substrates can be formed from, for example, aluminum, stainless steel, or nickel. The current collector preferably has a thickness of 5 to 20 μm. This is because in this range, the balance between electrode strength and weight reduction can be achieved.

2) Negative Electrode This negative electrode has a negative electrode current collector and a negative electrode layer carried on one or both surfaces of the negative electrode current collector and containing a negative electrode active material.

The negative electrode active material contains graphitized particles.

As the graphitized particles, the graphitized particles (A) or the graphitized particles (B) described below can be used.

Graphitized particles (A) The graphitized particles (A) have an abundance ratio of particles having a particle diameter of 5 μm or less of 5% by volume or less and a BET specific surface area by N ₂ adsorption of ² to 50 m ² / g. It is.

Graphitized particles having a particle size of 5 μm or less have low thermal stability, tend to cause gas generation during initial charge and discharge, and
In addition, it induces a reductive decomposition reaction of the non-aqueous electrolyte. When the abundance ratio of particles having a particle diameter of 5 μm or less in the graphitized particles exceeds 5% by volume, the amount of gas generated from the negative electrode during initial charge / discharge increases, so that the charge / discharge efficiency is reduced. Due to the reductive decomposition, the discharge capacity and the charge / discharge cycle life decrease. A more preferable range of the abundance ratio is 4.5.
% By volume or less. Further, when the abundance ratio is set to 0% by volume, the production of the graphitized particles becomes complicated, and the production cost may be increased. Therefore, the abundance ratio is set to 0.001% by volume to 3% by volume. Is more preferred. The most preferred range is 0.001% to 2% by volume.

The reason why the BET specific surface area of graphite particles by N ₂ adsorption is defined in the above range will be described. If the BET specific surface area by N ₂ adsorption is less than 2 m ² / g, the non-aqueous electrolyte adhesion area on the surface of the graphitized particles is insufficient, and the heterogeneous reaction is likely to occur, and the charge / discharge cycle life is shortened. On the other hand, the BET specific surface area by N ₂ adsorption is 50
If it exceeds m ² / g, the reductive decomposition reaction of the non-aqueous electrolyte and the formation of an inert film on the surface of the negative electrode are remarkable, so that the charge / discharge efficiency and the discharge capacity decrease, and a long life cannot be obtained.
A more preferable range of the specific surface area 2m ² / g~20m ² / g
In, still more preferably in the range of 2.5m ² / g~10m ² / g
In the most preferred range is 3m ² / g~10m ² / g.

Graphitized particles (B) The graphitized particles (B) satisfy the following expression (1).

0 ≦ P / S ≦ 2.5 (1) In the above (1), P is an abundance ratio (volume%) of particles having a particle diameter of 5 μm or less in the graphitized particles.
S is the BET specific surface area (m ² / g) of the graphitized particles due to N ₂ adsorption.

The reason for defining the value of P / S in the above range is as follows. If the P / S exceeds 2.5, the non-aqueous electrolyte adhesion area on the surface of the graphitized particles is insufficient, and a heterogeneous reaction is likely to occur. In addition, the amount of gas generated from the negative electrode during the initial charge / discharge increases, so that the charge / discharge efficiency tends to decrease. In addition, reductive decomposition of the non-aqueous electrolyte tends to occur. Therefore, if P / S exceeds 2.5, it may be difficult to obtain a high discharge capacity and an excellent charge / discharge cycle life. Further, when the P / S is set to 0, the production of the graphitized particles becomes complicated, and the production cost may be increased.
It is more desirable to make it 2.5 or less. A more preferred range is 0.1 ≦ P / S ≦ 1.

The content ratio P is 0.001% by volume to 5%.
It is preferable to be within the range of volume%. Existence ratio P is 5
If the content exceeds% by volume, the contact area between the nonaqueous electrolyte and the graphitized particles may be reduced, and a high capacity and a long life may not be obtained. A more preferable range of the existence ratio P is 0.001.
% By volume to 3% by volume.

In one embodiment of the invention, the specific surface area S is, 2m ² / g~10m ² /
It is preferred to be within the range of g. This is due to the following reasons. If the specific surface area S is less than 2 m ² / g, the contact area between the non-aqueous electrolyte and the graphitized particles may be reduced, and a high capacity and a long life may not be obtained. on the other hand,
If the specific surface area exceeds 10 m ² / g, a long life may not be obtained due to the reductive decomposition reaction of the non-aqueous electrolyte and the formation of an inert film on the negative electrode surface. A more preferred range of the specific surface area S is 3m ² / g~8m ² / g.

Among the graphitized particles (B), the most preferable one satisfies the expression (1), the abundance ratio P is 0.001% by volume to 5% by volume, and the specific surface area S is 2 m it is within the scope of the ² / ^{g~10m 2} / g. Such graphitized particles can significantly improve the discharge capacity and charge / discharge cycle life of the secondary battery.

The graphitized particles (A) and (B) desirably satisfy the characteristics described below.

The surfaces of the graphitized particles (A) and (B)
It is preferable that at least one element selected from the group consisting of B, O, Al and Si exists.

The graphitized particles (A) and (B) having oxygen atoms on the surface can be obtained, for example, by subjecting the graphitized particles to a heat treatment in an atmosphere containing oxygen to oxidize the surface of the graphitized particles. According to this oxidation treatment, the surface of the graphitized particles can be roughened, so that the specific surface area can be increased without reducing the particle size of the graphitized particles. Further, a functional group containing an oxygen atom may be bonded to the surface of the graphitized particles.

The graphitized particles (A) and (B) having at least one element selected from the group consisting of B, Al and Si on the surface are, for example, boron compounds (for example, B ₄ C, B ₂ O ₃ ) particles, alumina particles (Al ₂ O ₃ )
₃ ) and at least one additive selected from the group consisting of silicon compound (for example, SiO ₂ ) particles and graphitized particles. By this mixing, the additive particles are adsorbed on the surface of the graphitized particles.

On the other hand, the graphitized particles (A) and (B) having a boron atom on the surface are, for example, a precursor of a graphitized particle and a particle of a boron compound (for example, B ₄ C, B ₂ O ₃ ). Are mixed, and heat treatment is performed to obtain graphitized particles in which boron atoms are doped or dissolved.

The graphitized particles (A) and (B) preferably have a (002) plane spacing d ₀₀₂ of 0.337 nm by X-ray diffraction. A more preferred surface spacing d ₀₀₂ is
It is 0.336 nm or less.

The shape of the graphitized particles (A) and (B) can be spherical, granular or fibrous. The shape of the graphitized particles (A) and (B) is, for example, 1 such as spherical.
The types may be unified, or two or more different types of graphitized particles such as spherical and granular may be mixed and used. As described above, the negative electrode layer includes one or more types of graphitized particles selected from the group consisting of fibrous graphitized particles, spherical graphitized particles, and granular graphitized particles, thereby increasing the interfacial resistance of the negative electrode over a long period of time. Since the charge / discharge cycle life can be maintained at a low value, the charge / discharge cycle life can be improved.

The graphitized particles (A) and (B) may be composed of one or more kinds of particles selected from the group consisting of spherical particles, granular particles and fibrous particles, and flaky particles. . The content of the flaky particles in the graphitized particles (A) and (B) is preferably 50% by weight or less.

The average fiber length of the fibrous graphitized product is 5 to 5.
It is preferable that the thickness be in the range of 200 μm. A more preferred range is 10 to 50 μm.

The average fiber diameter of the above-mentioned fibrous graphitized product is 0.1.
It is preferable to set it in the range of 1 to 20 μm. A more preferred range is from 1 to 15 μm.

The average aspect ratio of the fibrous graphitized product is preferably in the range of 1.5 to 200. A more preferred range is from 1.5 to 50. However, the aspect ratio is the fiber length to the fiber diameter (fiber length / fiber diameter).
Is the ratio of

The average particle size of the spherical graphitized product is 1 to 10
It is preferable that the thickness be within the range of 0 μm. A more preferred range is 2 to 40 μm.

Major radius of the spherical graphitized material
The ratio of the minor radius (minor radius) to (minor radius / major radius) is
It is preferable to make it 1/10 or more. A more preferred range is 1/2 or more.

The above-mentioned granular graphitized material refers to a major diameter (major radiant).
us) to the minor radius (minor radius / major radius)
Means a graphitized powder having a shape in the range of 1/100 to 1. A more preferable range of the ratio is 1/1.
0 to 1.

The average particle size of the granular graphitized product is 1 to 10
It is preferable that the thickness be within the range of 0 μm. A more preferred range is 2 to 50 μm.

The graphitized particles (A) and (B) are produced, for example, by the method described below.

First, graphitized precursors such as mesophase pitch small spheres, mesophase pitch-based carbon fibers, vapor grown carbon fibers, granular carbon made from pitch or coke, and spherical carbon made from pitch or coke are used. 20
Heat treatment is performed at a temperature of 00 ° C. or higher to obtain graphitized particles, or granulated graphite is prepared as the graphitized particles. The surface of the graphitized particles is roughened by subjecting the obtained graphitized particles to a heat treatment in an atmosphere containing oxygen gas, or the surface of the graphitized particles is mechanically subjected to a roughening treatment. According to these surface roughening treatments, the specific surface area can be increased without reducing the particle diameter. Also,
A sufficient effect can be obtained by performing the surface roughening treatment on the spherical, granular and fibrous graphitized particles. Next, the graphitized particles (A) and (B) are obtained by sieving the graphitized particles using a cyclone or the like.

The binder has a function of binding the graphitized particles to each other and a function of binding the graphitized particles to the negative electrode current collector. Examples of such a binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR),
Carboxymethyl cellulose (CMC) or the like can be used. Positive electrode by the first and second manufacturing methods described below,
When the negative electrode and the separator are integrated, it is preferable to use a thermosetting resin as the binder, and PVdF is particularly preferable.

The compounding ratio of the graphitized product and the binder is preferably in the range of 90 to 98% by weight of the graphitized product and 2 to 20% by weight of the binder. In particular, the content of the graphitized material in the negative electrode is preferably in the range of 10 to 80 g / m ^{2 on} one side. The packing density is desirably in the range of 1.2 to 1.5 g / cm ³ .

The thickness of the negative electrode layer is preferably in the range of 10 to 150 μm. Here, the thickness of the negative electrode layer means the distance between the surface of the negative electrode layer facing the separator and the surface of the negative electrode layer contacting the current collector. When a negative electrode layer is supported on both surfaces of the negative electrode current collector, the thickness of one surface of the negative electrode layer is set to 10 to 150 μm, and the total thickness of the negative electrode layer is set to 20 μm.
It is desirable that the thickness be in the range of 300 μm. A more preferable range of the thickness of the negative electrode layer is 30 to 100 μm. By setting the thickness of the negative electrode layer in the range of 30 to 100 μm, large current discharge characteristics and cycle life can be significantly improved.

As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used.
These conductive substrates can be formed from, for example, copper, stainless steel, or nickel. Current collector thickness is 5
It is desirable that the thickness be about 20 μm. This is because in this range, the balance between electrode strength and weight reduction can be achieved.

3) Separator A porous separator is used as the separator.

Examples of the porous separator include a porous film containing polyethylene, polypropylene, cellulose, or polyvinylidene fluoride (PVdF), and a nonwoven fabric made of a synthetic resin. Among them, a porous film made of polyethylene, polypropylene, or both is preferable because the safety of the secondary battery can be improved.

The thickness of the separator is preferably in the range of 5 to 30 μm. A more preferred range is 10 to
25 μm.

The heat shrinkage of the separator when left at 120 ° C. for 1 hour is preferably 20% or less. More preferably, the heat shrinkage is 15% or less.

The porosity of the separator is preferably in the range of 30 to 70%. A more preferred range of porosity is 35-70%.

The separator has an air permeability of 500 seconds.
/ 100cm^ThreeThe following is preferred. Air permeability
Is 100cm^ThreeOf air passes through the porous sheet
It means the time (second) required. Air permeability 500 seconds /
100cm^ThreeExceeds the limit, high
It may be difficult to obtain um ion mobility.
The lower limit of the air permeability is 30 seconds / 100 cm.^ThreeTo
Is preferred. Air permeability 30 seconds / 100cm
^ThreeIf it is less than the above, sufficient separator strength cannot be obtained.
This is because there is a danger that The upper limit of air permeability is 150
Sec / 100cm ^ThreeIs more preferable. Also below
Limit value is 50 seconds / 100cm^ThreeMore preferable to
No.

4) Non-aqueous electrolyte This non-aqueous electrolyte contains a non-aqueous solvent in which the electrolyte is dissolved. The viscosity of the non-aqueous solvent at 20 ° C. is 4 cP or more. Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte composed of the non-aqueous solvent and a gel electrolyte in which the liquid non-aqueous electrolyte and a polymer material are combined.

When the viscosity at 20 ° C. of the non-aqueous solvent in which the electrolyte is dissolved is less than 4 cP, the vapor pressure of the non-aqueous electrolyte in a high-temperature environment (60 ° C. or higher) increases, and the non-aqueous electrolyte is charged at the initial charging and discharging The amount of gas generated in the environment increases, and the swelling of the container increases. By setting the viscosity at 20 ° C. to 4 cP or more, the vapor pressure of the nonaqueous electrolyte in a high-temperature environment (60 ° C. or more) can be reduced. Less,
Swelling of the container can be suppressed. A more preferred range of viscosity at 20 ° C. is 5 cP or more.

Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC) and vinylene carbonate (VC);
-Butyrolactone (BL), diethyl carbonate (D
Chain carbonates such as EC).
Among them, a non-aqueous solvent containing γ-butyrolactone as one component is preferable. A non-aqueous electrolyte containing such a non-aqueous solvent can improve lithium ion conductivity and stability in a high-temperature environment. In particular, as a non-aqueous solvent,
EC and BL, EC and PC and BL, EC and BL and VC, E
C and PC and BL and VC, EC and DEC, EC and PC and D
It is desirable to use a mixed solvent of EC. The abundance ratio of EC in the six kinds of mixed solvents is 10 to 5 respectively.
It is preferable that it is in the range of 0% by volume.

As a non-aqueous solvent, γ-butyrolactone (γ
BL), when using γ-
The volume ratio of butyrolactone (γBL) is preferably set to 50% by volume or more of the whole non-aqueous solvent. Since the non-aqueous electrolyte including such a non-aqueous solvent has high thermal stability, it is possible to suppress abnormal heat generation of the battery and further improve safety. If the volume ratio of γBL is less than 50% by volume, the amount of gas generated at high temperatures increases, and it may be difficult to suppress the expansion of the container. Further, when the solvent mixed with γBL is a cyclic carbonate (for example, ethylene carbonate), the volume ratio of the cyclic carbonate is relatively high, so that the solvent viscosity is increased, the conductivity is reduced, and the charge / discharge cycle characteristics are reduced. And the large current discharge characteristics deteriorate. On the other hand, if the volume ratio of γBL exceeds 95% by volume, a reaction between the negative electrode and γBL may occur and charge / discharge cycle characteristics and safety may be reduced.
The volume ratio of L is preferably in the range of 50 to 95% by volume. A more preferable range of the volume ratio of γBL is
It is 55% by volume or more and 75% by volume or less. Within this range, the effect of suppressing gas generation during high-temperature storage becomes higher.

The electrolyte may be, for example, lithium perchlorate.
(LiClO_Four), Lithium hexafluorophosphate (Li
PF₆), Lithium tetrafluoroborate (LiBF_Four), Rokufu
Lithium arsenide (LiAsF)₆), Trifluorometa
Lithium sulfonate (LiCF_ThreeSO_Three), Bistriflu
Lithium olomethylsulfonylimide [LiN (CF _Three
SO_Two)_Two] And other lithium salts. Among them, L
iPF₆, LiBF_Four, LiAsF₆, LiClO_FourUsing
Preferably.

The amount of the electrolyte dissolved in the nonaqueous solvent is 1 to
Desirably, it is 3 mol / L. A more preferred range is 1.2 to 2 mol / L.

The gel non-aqueous electrolyte has a viscosity at 20 ° C. of 4 by dissolving the electrolyte in a non-aqueous solvent.
After preparing a liquid non-aqueous electrolyte having a cP or more, this liquid non-aqueous electrolyte and a polymer are mixed and subjected to a heat treatment to be gelled.

Examples of the polymer include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), and polyvinyl chloride (P
At least one polymer selected from VC) and polyacrylate (PMMA) can be used. The weight ratio of the polymer in the non-aqueous electrolyte is 0.5 to 2
It is preferable to be within the range of 0% by weight.

When a liquid non-aqueous electrolyte is used, the amount of the liquid non-aqueous electrolyte is 100 mAh per unit cell capacity.
It is preferably 0.2 to 0.6 g per unit. The more preferable range of the mass of the liquid non-aqueous electrolyte is 0.4 to 0.55 g.
/ 100 mAh.

5) Container The shape of the container can be, for example, a cylindrical shape with a bottom, a rectangular tube with a bottom, a bag shape, or the like.

The container can be formed from, for example, a film material, a metal plate or the like.

A container (metal can) made of a metal plate
For example, it can be formed from aluminum, iron, stainless steel, nickel, or the like.

Examples of the film material constituting the container include a metal film, a resin film such as a thermoplastic resin, and a composite film including a metal layer and a resin layer (for example, one or both sides of a flexible metal layer may be used). A laminated film covered with a resin layer such as a thermoplastic resin). Among them, the laminated film is
It is desirable because it is lightweight, has high strength, and can prevent intrusion of moisture from the outside.

The metal film can be made of, for example, aluminum, iron, stainless steel, nickel, or the like.

The resin layer constituting the composite film can be formed, for example, from a thermoplastic resin. Examples of such thermoplastic resins include polyolefins such as polyethylene and polypropylene. The resin layer can be formed from one type of resin or two or more types of resins.

The metal layer of the composite film can be formed of, for example, aluminum, iron, stainless steel, nickel or the like. The metal layer can be formed from one kind of metal or two or more kinds of metals. Among them,
It is desirable to form from aluminum which can prevent water from entering the inside of the battery.

The container manufactured using the composite film is sealed by, for example, heat sealing. For this reason, it is desirable to arrange a thermoplastic resin on the inner surface of the container. The melting point of the thermoplastic resin is preferably 120 ° C. or higher, more preferably 140 ° C. to 250 ° C. Examples of the thermoplastic resin include polyolefins such as polyethylene and polypropylene. In particular, it is desirable to use polypropylene having a melting point of 150 ° C. or higher because the sealing strength of the heat seal portion is increased.

The thickness of the film material and the metal plate is 0.25
mm or less. The thickness of the film material and metal plate is 0.2
If it exceeds 5 mm, the improvement of the volume energy density and the weight energy density of the nonaqueous electrolyte secondary battery is hindered. Further, it is more preferable that the thickness of the film material and the metal plate be 0.05 mm or more and 0.25 mm or less. By setting the thicknesses of the film material and the metal plate in the above ranges, the strength of the container can be ensured, and the volume energy density and the weight energy density of the nonaqueous electrolyte secondary battery can be improved. . A particularly desirable thickness range is 0.05 mm or more and 0.2 mm or less. This makes it possible to reduce the thickness and weight of the battery while ensuring the strength of the container.

Hereinafter, an example of a method for manufacturing a nonaqueous electrolyte secondary battery according to the present invention will be described. However, the method for manufacturing a nonaqueous electrolyte secondary battery according to the present invention is not limited to the following embodiment.

(First Production Method) The separator is interposed between the positive electrode and the negative electrode and wound into a flat shape, or the positive electrode and the negative electrode are bent one or more times with the separator interposed therebetween. After the obtained flat article is stored in a container, the binder contained in the positive electrode and the negative electrode is thermally cured by applying heat and pressure to integrate the positive electrode, the negative electrode, and the separator. After injecting the liquid non-aqueous electrolyte into the container, the opening of the container is sealed to assemble a thin non-aqueous electrolyte secondary battery.

The heating and pressurizing are performed in a high-pressure reduced pressure atmosphere (including vacuum) of 30 ° C. or more or a normal pressure atmosphere, and the applied pressure is 0.05 kg / cm ² or more and 30 kg / cm ² or more.
cm ² or less.

The heating and pressurizing atmosphere is 60 ° C. to 100 ° C.
The use of a reduced pressure atmosphere (including vacuum) at a temperature of ° C. is preferable because the electrode group can be dried at the same time.

More preferable pressure in heating and pressurizing is
It is 0.01 to 15 kg / cm ² . Further, the temperature of the atmosphere in which the heating and pressurizing is performed is more preferably in the range of 60C to 100C.

As the pressing method, a press such as a flat plate press or a roll press, or insertion into a holder having a predetermined thickness can be employed.

(Second Manufacturing Method) The separator is interposed between the positive electrode and the negative electrode and wound into a flat shape, or the positive electrode and the negative electrode are bent one or more times with the separator interposed therebetween. By applying heat and pressure to the obtained flat-shaped product, the binder contained in the positive electrode and the negative electrode is thermoset, and the positive electrode, the negative electrode, and the separator are integrated. The thin-film non-aqueous electrolyte secondary battery is assembled by housing the electrode group in a container, injecting a liquid non-aqueous electrolyte into the container, and sealing the opening of the container.

The heating and pressurizing can be performed by the same method as described in the first manufacturing method.

(Third Manufacturing Method) An electrode group is manufactured by interposing a porous sheet as a separator between a positive electrode and a negative electrode. The electrode group is housed in a container. A polymer having adhesive properties is dissolved in a solvent, and the obtained solution is injected into the electrode group in the container, and the solution is impregnated into the electrode group.
Next, after applying heat and pressure to the container, a liquid non-aqueous electrolyte is injected into the container, and the opening of the container is sealed to assemble a thin non-aqueous electrolyte secondary battery.

The heating and pressurizing can be performed by the same method as described in the first manufacturing method.

It is desirable to use an organic solvent having a boiling point of 200 ° C. or less as the solvent. Examples of such an organic solvent include dimethylformamide (boiling point: 153 ° C.)
Can be mentioned. The lower limit of the boiling point of the organic solvent is preferably set to 50 ° C. The upper limit of the boiling point is 1
The temperature is more preferably set to 80 ° C, and the lower limit of the boiling point is more preferably set to 100 ° C.

The concentration of the adhesive polymer in the solution is preferably in the range of 0.05 to 2.5% by weight. A more preferable range of the concentration is 0.1 to 1.5% by weight.
It is.

The amount of the solution to be injected may be in the range of 0.1 to 2 mL per 100 mAh of battery capacity, when the concentration of the adhesive polymer in the solution is 0.1 to 2.5% by weight. preferable. A more preferable range of the injection amount is 0.15 to 1 mL per 100 mAh of battery capacity.

The total amount of the adhesive polymer contained in the battery manufactured by the third method is 100 battery capacity.
Preferably, the amount is 0.1 to 6 mg per mAh. A more preferred range of the total amount of the polymer having adhesiveness is 0.2 to 1 mg per 100 mAh of battery capacity.

In the above-described third manufacturing method, the solution in which the polymer having the adhesive property is dissolved is injected after the electrode group is stored in the container. Is also good. In this case, first, an electrode group is prepared by interposing a separator between the positive electrode and the negative electrode. After the electrode group is impregnated with the solution, the electrode group is heated and dried by applying heat and pressure under the same conditions as described in the first manufacturing method described above to evaporate the solvent of the solution. , To form an electrode group having a predetermined thickness. After storing such an electrode group in a container, a liquid non-aqueous electrolyte is injected, and sealing is performed. Thus, a thin non-aqueous electrolyte secondary battery can be manufactured.

A thin lithium ion secondary battery which is an example of the non-aqueous electrolyte secondary battery according to the present invention will be described with reference to FIGS. FIG. 1 is a sectional view showing a thin lithium ion secondary battery as an example of the nonaqueous electrolyte secondary battery according to the present invention, and FIG. 2 is an enlarged sectional view showing a portion A in FIG.

As shown in FIG. 1, an electrode group 2 is housed in a container 1 formed by processing a film material including a resin layer into a bag shape. The electrode group 2 has a structure in which a laminate including a positive electrode, a separator, and a negative electrode is wound into a flat shape.
X indicates the thickness (wall thickness) of the wall of the container 1. The laminate includes, from the lower side in FIG. 2, a separator 3, a positive electrode layer 4, a positive electrode current collector 5 and a positive electrode 6 including a positive electrode layer 4, a separator 3, a negative electrode layer 7, a negative electrode current collector 8, and a negative electrode layer 7. , A separator 3, a positive electrode layer 4, a positive electrode current collector 5, a positive electrode 6 having a positive electrode layer 4, a separator 3, a negative electrode 9 having a negative electrode layer 7 and a negative electrode current collector 8 are laminated in this order. It has the structure which was done. A negative electrode current collector 8 is located at the outermost periphery of the electrode group 2. The non-aqueous electrolyte is contained in the container 1. One end of the strip-shaped positive electrode lead 10 is connected to the positive electrode current collector 5 of the electrode group 1,
The other end extends from the container 1. On the other hand, one end of the strip-shaped negative electrode lead 11 is connected to the negative electrode current collector 8 of the electrode group 1, and the other end is extended from the container 1.

The first non-aqueous electrolyte secondary battery according to the present invention described above comprises a container, a positive electrode housed in the container, and a negative electrode housed in the container and containing a negative electrode active material. A non-aqueous electrolyte secondary battery including a non-aqueous electrolyte accommodated in the container, wherein the wall thickness of the container is 0.25 mm or less, and the negative electrode active material has a particle diameter of 5 μm.
The content ratio of the following particles is 5% by volume or less and N ₂
The non-aqueous electrolyte contains graphitized particles having a BET specific surface area of ² to 50 m ² / g by adsorption, and the non-aqueous electrolyte has a viscosity of 4 cP or more at 20 ° C. and contains a non-aqueous solvent in which the electrolyte is dissolved. It is a feature.

According to the present invention, it is possible to realize a non-aqueous electrolyte secondary battery in which gas generation during initial charge and discharge and storage at high temperature is suppressed, swelling of the container is suppressed, and discharge capacity and cycle life are excellent. it can.

A non-aqueous electrolyte containing an electrolyte-dissolved non-aqueous solvent having a viscosity of 4 cP or more at 20 ° C. can reduce the vapor pressure in a high-temperature environment of 60 ° C. or more. Generation of gas under the environment can be suppressed, and expansion and deformation of the container can be suppressed. However, such a non-aqueous electrolyte has a low permeation rate to the negative electrode, and also has a high surface tension, so that the affinity with the graphite material having a smooth surface is poor, and the interface resistance between the non-aqueous electrolyte and the negative electrode increases, Lithium metal precipitates on the negative electrode surface, leading to a reduction in cycle life. When fine particles having a particle diameter of 5 μm or less are used as the graphite material, the specific surface area of the graphite material increases, and more nonaqueous electrolyte can be attached to the graphite material. However, fine particles having a particle diameter of 5 μm or less are thermally stable. The non-aqueous electrolyte is easily reduced and decomposed, and the amount of gas generated from the negative electrode during initial charge and discharge is increased.

As in the invention of the present application, by using graphitized particles having an abundance ratio of particles having a particle diameter of 5 μm or less of 5% by volume or less and a BET specific surface area by N ₂ adsorption of ² to 50 m ² / g. Dispersing the non-aqueous electrolyte evenly on the surface of the graphitized particles, while ensuring the thermal stability of the graphitized particles and suppressing the reductive decomposition of the non-aqueous electrolyte and the generation of gas from the negative electrode during initial charge and discharge Can be. As a result, the interface resistance between the negative electrode and the non-aqueous electrolyte can be reduced, so that the discharge capacity and cycle life of the secondary battery can be improved.

Therefore, according to the present invention, a non-aqueous electrolyte which can be used in a thin container because it generates little gas at the time of initial charge / discharge and at the time of use in a high temperature environment, and is excellent in discharge capacity and cycle life. A secondary battery can be realized.

A second nonaqueous electrolyte secondary battery according to the present invention includes a container, a positive electrode housed in the container, and a negative electrode housed in the container and containing a negative electrode active material.
In a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte accommodated in the container, a wall thickness of the container is 0.25
mm or less, the negative electrode active material contains graphitized particles satisfying the following formula (1), and the nonaqueous electrolyte contains
It contains a non-aqueous solvent having a viscosity at 4 ° C. of 4 cP or more in which an electrolyte is dissolved.

0 ≦ P / S ≦ 2.5 (1) In the above (1), P is an abundance ratio (volume%) of particles having a particle diameter of 5 μm or less in the graphitized particles.
S is the BET specific surface area (m ² / g) of the graphitized particles due to N ₂ adsorption.

According to the present invention, the contact area between the graphitized particles and the non-aqueous electrolyte is increased while minimizing the generation of gas from the negative electrode during initial charge and discharge and the reductive decomposition of the non-aqueous electrolyte. The interface impedance of the electrolyte can be reduced. As a result, the discharge capacity and charge / discharge cycle life of the secondary battery can be further improved.

In the first and second non-aqueous electrolyte secondary batteries according to the present invention, B, O, A
Since the presence of at least one element selected from the group consisting of l and Si can increase the wettability of the negative electrode with the nonaqueous electrolyte, the contact area between the negative electrode and the nonaqueous electrolyte can be increased. can do. As a result, the charge / discharge reaction at the negative electrode proceeds uniformly, so that the cycle performance can be further improved.

[0102]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Positive Electrode> 91% by weight of lithium cobalt oxide powder having a composition represented by LiCoO ₂ was added to acetylene black 2
% By weight, 3% by weight of graphite, 4% by weight of polyvinylidene fluoride (PVdF) and an N-methylpyrrolidone (NMP) solution were added and mixed to prepare a slurry. The obtained slurry was applied to a 10-μm-thick aluminum foil current collector, dried, and pressed to obtain a positive electrode having an electrode density of 3.0 g / cm ³ and a thickness of 120 μm.

<Preparation of Negative Electrode> 3000 ° C.
Mesophase pitch-based carbon fiber (average fiber diameter: 8 μm, average fiber length: 20 μm, spacing (d ₀₀₂ ) between (002) planes by X-ray diffraction is 0.3360 nm)
The powder was heat-treated in an air flow at 700 ° C. for 8 hours to oxidize the surface, and then fine powder was removed with a cyclone. The particle size distribution of the obtained fibrous graphitized particles was measured with a laser diffractometer, and the particle diameter in the graphitized particles was 5 μm.
The abundance ratio of the following particles was determined, and the results are shown in Table 1 below. The BET specific surface area of the graphitized particles measured by N ₂ adsorption was measured, and the results are shown in Table 1 below. further,
The relational expression P / S between the abundance ratio P (% by volume) and the specific surface area S (m ² / g) was determined, and the results are shown in Table 1 below.

93% by weight of the graphitized particles, 7% by weight of polyvinylidene fluoride (PVdF) as a binder,
An NMP solution was added and mixed to prepare a slurry. The obtained slurry was applied to both sides of a current collector made of a copper foil having a thickness of 10 μm, dried, and pressed to collect a negative electrode layer having an electrode density of 1.40 g / cm ³ and a thickness of 60 μm. A negative electrode supported on both surfaces of the electric body was produced. Therefore, the total thickness of the negative electrode layer is 120 μm.

<Preparation of Flat Shaped Electrode Group> Thickness 27 μm
m, a porosity of 50%, and an air permeability of 90 seconds / 100 cm ³ A polyethylene separator was prepared. After the separator is interposed between the positive electrode and the negative electrode, the separator is spirally wound and then formed into a flat shape, having a thickness of 2.7 mm and a width of 30 m.
m, a flat electrode group having a height of 50 mm was prepared.

<Preparation of Liquid Nonaqueous Electrolyte> 1.5 mol of lithium tetrafluoroborate (LiBF ₄ ) was mixed in a mixed solvent of ethylene carbonate (EC) and γ-butyrolactone (γBL) (mixing volume ratio 40:60). / L dissolved to prepare a liquid non-aqueous electrolyte. The viscosity at 20 ° C. of the liquid nonaqueous electrolyte was 6 cP.

<Formation of Electrode Group> A laminate film having a thickness of 0.1 mm in which both surfaces of an aluminum foil were covered with polypropylene was prepared and formed into a bag to obtain a container. The flat electrode group is accommodated in this, and the battery thickness is 2.7 m.
The battery was pressed at 90 ° C. for 1 minute so as to be fixed at m. At this time, the pressure applied to the electrode group was 20 kg / cm ² .

Next, the electrodes in the laminate film were vacuum-dried at 80 ° C. for 12 hours. 2 g of the liquid non-aqueous electrolyte was injected into the electrode group in the laminate film, and had a structure shown in FIGS.
A thin nonaqueous electrolyte secondary battery having a thickness of 32 mm, a width of 32 mm, and a height of 55 mm was assembled.

Example 2 Spherical coke was heat-treated at 3000 ° C. to obtain a powder of spherical graphite having an average particle size of 10 μm (plane spacing (d ₀₀₂ ) of (002) plane by X-ray diffraction (d ₀₀₂ ) of 0.3355 nm). Obtained. The surface of the spherical graphite powder was oxidized by subjecting it to a heat treatment at 700 ° C. for 8 hours in air, and then the fine powder was removed by cyclone treatment to obtain spherical graphitized particles. The particle size distribution of the obtained graphitized particles was measured in the same manner as described in Example 1 above,
The abundance ratio of particles having a particle diameter of 5 μm or less in the graphitized particles was determined, and the results are shown in Table 1 below. The BET specific surface area of the graphitized particles measured by N ₂ adsorption was measured, and the results are shown in Table 1 below. Furthermore, the existence ratio P (volume%)
A relational expression P / S between the specific surface area S and the specific surface area S (m ² / g) was obtained, and the results are shown in Table 1 below.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that such graphitized particles were used.

(Example 3) Granular graphite having an average particle size of 8 μm obtained by finely pulverizing and granulating natural graphite (having a (002) plane spacing (d ₀₀₂ ) of 0.3354 n by X-ray diffraction).
The surface was oxidized by subjecting the powder of m) to a heat treatment at 700 ° C. for 15 hours in air, and then the fine powder was removed by cyclone treatment to obtain granular graphitized particles. The particle size distribution of the obtained graphitized particles was measured in the same manner as described in Example 1 above, and the abundance ratio of the particles having a particle diameter of 5 μm or less in the graphitized particles was determined. Shown in The BET specific surface area of the graphitized particles measured by N ₂ adsorption was measured, and the results are shown in Table 1 below. Further, a relational expression P between the abundance ratio P (volume%) and the specific surface area S (m ² / g)
/ S was determined, and the results are shown in Table 1 below.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that such graphitized particles were used.

(Example 4) Mesophase small spheres were
Spheroidal graphite having an average particle size of 15 μm which was heat-treated at 0 ° C. (plane spacing (d ₀₀₂ ) of (002) plane by X-ray diffraction was 0.335.
(4 nm) powder was subjected to heat treatment at 700 ° C. for 8 hours in air to oxidize the surface, and then fine powder was removed by cyclone treatment to obtain spherical graphitized particles. The particle size distribution of the obtained graphitized particles was measured in the same manner as described in Example 1 above, and the abundance ratio of the particles having a particle diameter of 5 μm or less in the graphitized particles was determined. Shown in The BET specific surface area of the graphitized particles measured by N ₂ adsorption was measured, and the results are shown in Table 1 below. Further, a relational expression P between the abundance ratio P (volume%) and the specific surface area S (m ² / g)
/ S was determined, and the results are shown in Table 1 below.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that such graphitized particles were used.

Example 5 A fibrous graphitized product (average fiber diameter: 8 μm, average fiber length: 15 μm) was obtained by subjecting mesophase pitch-based carbon fiber powder to heat treatment at 3000 ° C.
m, a powder having a (002) plane spacing (d ₀₀₂ ) of 0.3358 nm by X-ray diffraction was obtained. The obtained powder was subjected to a heat treatment at 700 ° C. for 8 hours in air to oxidize the surface, and then fine powder was removed by cyclone treatment to obtain fibrous graphitized particles. The particle size distribution of the obtained graphitized particles was measured in the same manner as described in Example 1 above, and the abundance ratio of the particles having a particle diameter of 5 μm or less in the graphitized particles was determined. Shown in The BET specific surface area of the graphitized particles measured by N ₂ adsorption was measured, and the results are shown in Table 1 below. Further, a relational expression P / S between the abundance ratio P (% by volume) and the specific surface area S (m ² / g) was obtained, and the results are shown in Table 1 below.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that such graphitized particles were used.

(Example 6) A powder of mesophase pitch-based carbon fiber was subjected to a heat treatment at 3000 ° C to obtain a fibrous graphitized material (average fiber diameter: 8 µm, average fiber length: 25 µm).
m, a powder having a (002) plane spacing (d ₀₀₂ ) of 0.3358 nm by X-ray diffraction was obtained. The obtained powder was subjected to a heat treatment at 700 ° C. for 8 hours in air to oxidize the surface, and then fine powder was removed by cyclone treatment to obtain fibrous graphitized particles. The particle size distribution of the obtained graphitized particles was measured in the same manner as described in Example 1 above, and the abundance ratio of the particles having a particle diameter of 5 μm or less in the graphitized particles was determined. Shown in The BET specific surface area of the graphitized particles measured by N ₂ adsorption was measured, and the results are shown in Table 1 below. Further, a relational expression P / S between the abundance ratio P (% by volume) and the specific surface area S (m ² / g) was obtained, and the results are shown in Table 1 below.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that such graphitized particles were used.

Example 7 3000 ° C. was added to a mesophase pitch carbon fiber powder to which 10% by weight of B ₂ O ₃ powder was added.
By heat treatment, the fibrous graphitized particles in which boron atoms are dissolved (average fiber diameter is 8 μm, average fiber length is 13 μm, and the plane spacing (d) of (002) plane by X-ray diffraction (d
₀₀₂ ) was obtained at 0.3354 nm). The surface was oxidized by subjecting the fibrous graphitized particles to heat treatment at 800 ° C. for 3 hours in air, and then fine powder was removed by cyclone treatment. The particle size distribution of the obtained graphitized particles was measured in the same manner as described in Example 1 above, and the abundance ratio of the particles having a particle diameter of 5 μm or less in the graphitized particles was determined. Shown in In addition, the BET specific surface area of the graphitized particles measured by N ₂ adsorption was measured.
Shown in Furthermore, the existence ratio P (volume%) and the specific surface area S
The relational expression P / S with (m ² / g) was determined, and the results are shown in Table 1 below.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that such graphitized particles were used.

Example 8 3000 ° C. was added to a mesophase pitch-based carbon fiber powder to which 10% by weight of B ₂ O ₃ powder was added.
By heat treatment, the fibrous graphitized particles in which boron atoms are dissolved (average fiber diameter is 8 μm, average fiber length is 13 μm, and the plane spacing (d) of (002) plane by X-ray diffraction (d
₀₀₂ ) was obtained at 0.3354 nm). The surface was oxidized by subjecting the fibrous graphitized particles to heat treatment at 800 ° C. for 3 hours in air, and then fine powder was removed by cyclone treatment. The particle size distribution of the obtained graphitized particles was measured in the same manner as described in Example 1 above, and the abundance ratio of the particles having a particle diameter of 5 μm or less in the graphitized particles was determined. Shown in In addition, the BET specific surface area of the graphitized particles measured by N ₂ adsorption was measured.
Shown in Furthermore, the existence ratio P (volume%) and the specific surface area S
The relational expression P / S with (m ² / g) was determined, and the results are shown in Table 1 below.

98% by weight of such graphitized particles were mixed with 2% by weight of silica (SiO ₂ ) powder having an average particle size of 0.4 μm, and 93% by weight of the obtained mixed powder was mixed with polyvinylidene fluoride as a binder. (PVdF) 7% by weight and an NMP solution were added and mixed to prepare a slurry. The obtained slurry was applied to both sides of a current collector made of a copper foil having a thickness of 10 μm, dried, and pressed to obtain an electrode density of 1.
A negative electrode having a negative electrode layer of 35 g / cm ³ and a thickness of 60 μm was supported on both surfaces of the current collector. Therefore, the total thickness of the negative electrode layer is 120 μm.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the obtained negative electrode was used.

Example 9 Silica (SiO 2)_Two) Powder fee
Instead, alumina (Al) having an average particle size of 0.4 μm_TwoO _Three)powder
Except for using the powder, the same as in Example 8 described above
A thin non-aqueous electrolyte secondary battery was manufactured.

Example 10 3000 ° C. as a graphitized material
Mesophase pitch-based carbon fiber (average fiber diameter: 8 μm, average fiber length: 20 μm, spacing (d ₀₀₂ ) between (002) planes by X-ray diffraction is 0.3360 nm)
The powder was heat-treated at 700 ° C. for 8 hours in an air flow to oxidize the surface and obtain fibrous graphitized particles. A mixture of 80% by weight of the fibrous graphitized particles and 20% by weight of flaky natural graphite having an average particle diameter of 6 μm (d ₀₀₂ is 0.3354 nm) is used to remove fine powder with a cyclone to obtain mixed graphitized particles. Was.

The particle size distribution of the obtained mixed graphitized particles was measured in the same manner as described in Example 1 above, and the proportion of particles having a particle size of 5 μm or less in the mixed graphitized particles was determined. The results are shown in Table 1 below. Further, the BET specific surface area of the mixed graphitized particles by N ₂ adsorption was measured,
The results are shown in Table 1 below. Further, a relational expression P / S between the abundance ratio P (% by volume) and the specific surface area S (m ² / g) was obtained, and the results are shown in Table 1 below.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that such graphitized particles were used.

(Example 11) <Preparation of gelled non-aqueous electrolyte> A liquid non-aqueous electrolyte similar to that described in Example 1 described above, and polyvinylidene fluoride hexafluoropropylene (PVdF-HEP)
Was dissolved in tetrahydroxyfuran (THF) and mixed with each other to prepare a paste. The obtained paste was applied to a substrate and dried to obtain a thin film.

<Preparation of Electrode Group> A positive electrode similar to that described in Example 1 and a negative electrode similar to that described in Example 1 were spirally wound therebetween with the thin film interposed therebetween. Thereafter, the electrode was formed into a flat shape to produce an electrode group.

This electrode group was immersed in the above-mentioned liquid nonaqueous electrolyte, and the thin film was plasticized under reduced pressure to obtain an electrode group in which a gel nonaqueous electrolyte layer was interposed between the positive electrode and the negative electrode.

A laminate film similar to that described in Example 1 was formed into a bag, and the electrode group was housed in the bag. The thickness was 2.7 mm, the width was 32 mm, and the height was 55.
mm thin non-aqueous electrolyte secondary battery was assembled.

(Comparative Example 1) A powder of mesophase pitch-based carbon fiber which had been pulverized so that the abundance ratio of fine particles having a particle size of 5 μm or less became 6% by volume was heat-treated at 3000 ° C. to obtain a fibrous graphitized material (average A powder having a fiber diameter of 8 μm, an average fiber length of 15 μm, and a (002) plane spacing (d ₀₀₂ ) of 0.3358 nm by X-ray diffraction) was obtained. A thin non-aqueous electrolyte secondary battery was assembled in the same manner as described in Example 1 except that the obtained fibrous graphitized product was used.

(Comparative Example 2) A spherical coke having an average particle diameter of 10 μm was obtained by heat-treating spherical coke having been subjected to pulverization so that the proportion of fine particles having a particle diameter of 5 μm or less to be 6% by volume at 3000 ° C. A powder having a (002) plane spacing (d ₀₀₂ ) of 0.3355 nm by diffraction) was obtained.
A thin non-aqueous electrolyte secondary battery was assembled in the same manner as described in Example 1 except that this spheroidal graphite was used.

Comparative Example 3 Granular graphite having an average particle size of 8 μm obtained by granulating natural graphite ((002) by X-ray diffraction)
The fine powder in the powder having a plane spacing (d ₀₀₂ ) of 0.3354 nm) was removed, and the proportion of fine particles of 5 μm or less in the graphite powder was set to 15% by volume. A thin non-aqueous electrolyte secondary battery was assembled in the same manner as described in Example 1 except that such a graphite powder was used.

(Comparative Example 4) Fine powder in a powder of natural graphite having an average particle size of 10 μm (the spacing (d _{00 2} ) of the (002) plane (d _{00 2} ) by X-ray diffraction was 0.3354 nm) was removed, and the graphite powder was removed. The content ratio of the fine particles having a size of 5 μm or less was set to 15% by volume. A thin non-aqueous electrolyte secondary battery was assembled in the same manner as described in Example 1 except that such a graphite powder was used.

The obtained Examples 1 to 11 and Comparative Examples 1 to 4
Of the secondary battery was charged to 4.2 V at 1 C for 2 hours, and then subjected to a charge / discharge cycle test in which the battery was discharged to 3 V at 1 C. The initial capacity and the capacity retention after 500 cycles (assuming the initial capacity as 100%) were obtained. The measurement was performed and the results are shown in Table 1 below.

[0138]

[Table 1]

As is clear from Table 1, Examples 1 to 11
It can be understood that the secondary battery of No. has a higher discharge capacity and a higher capacity retention after 500 cycles than the secondary batteries of Comparative Examples 1 to 4.

[0140]

As described in detail above, according to the present invention,
A container having a wall thickness of 0.25 mm or less can be used as an exterior material, and a high-capacity, long-life nonaqueous electrolyte secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a thin lithium ion secondary battery as an example of a nonaqueous electrolyte secondary battery according to the present invention.

FIG. 2 is an enlarged sectional view showing a portion A in FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... container, 2 ... electrode group, 3 ... separator, 6 ... positive electrode, 9 ... negative electrode, X ... thickness of container.

Continued on the front page F-term (reference) 5H011 AA13 CC06 CC10 KK01 5H029 AJ03 AJ05 AJ07 AK02 AK03 AK05 AL07 AM03 AM05 AM07 BJ02 BJ04 BJ14 CJ25 DJ02 DJ15 DJ16 HJ01 HJ05 HJ07 HJ10 5H050 AA07 FAA13CA08 HA01 HA05 HA07 HA10

Claims (8)

[Claims] A non-aqueous electrolyte including a container, a positive electrode housed in the container, a negative electrode housed in the container and containing a negative electrode active material, and a non-aqueous electrolyte housed in the container. In the water-electrolyte secondary battery, the wall thickness of the container is 0.25 mm or less, and the negative electrode active material has an abundance ratio of particles having a particle diameter of 5 μm or less of 5% by volume or less and a BET ratio by N ₂ adsorption. It contains graphitized particles having a surface area of ² to 50 m ² / g,
The non-aqueous electrolyte secondary battery includes a non-aqueous solvent having a viscosity of 4 cP or more at 20 ° C. in which the electrolyte is dissolved. 2. A non-equipment comprising a container, a positive electrode housed in the container, a negative electrode housed in the container and containing a negative electrode active material, and a non-aqueous electrolyte housed in the container. In the water electrolyte secondary battery, the thickness of the wall of the container is 0.25 mm or less, the negative electrode active material contains graphitized particles satisfying the following formula (1), and the non-aqueous electrolyte is 20 A non-aqueous electrolyte secondary battery comprising a non-aqueous solvent having a viscosity at 4 ° C. of 4 cP or more and in which an electrolyte is dissolved. 0 ≦ P / S ≦ 2.5 (1) In the above (1), P is an abundance ratio (volume%) of particles having a particle diameter of 5 μm or less in the graphitized particles,
S is the BET specific surface area (m ² / g) of the graphitized particles due to N ₂ adsorption. 3. The presence ratio P is 0.001% by volume or more.
The non-aqueous electrolyte secondary battery according to claim 2, wherein the content is within a range of 5% by volume. 4. The specific surface area S is 2 m ² / g to 10 m ^2.
The non-aqueous electrolyte secondary battery according to claim 2, wherein the ratio is within the range of / g. 5. B, O, A on the surface of the graphitized particles
3. The non-aqueous electrolyte secondary battery according to claim 1, wherein at least one element selected from the group consisting of 1 and Si exists. 6. The shape of the graphitized particles includes at least one type selected from the group consisting of spherical, granular, and fibrous shapes, and a flaky shape. The non-aqueous electrolyte secondary battery according to the above. 7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte has a liquid or gel form. 8. The method according to claim 1, wherein the surface of the graphitized particles is subjected to a surface roughening treatment.
The nonaqueous electrolyte secondary battery according to the above.