JP2003123740A - Negative electrode for secondary battery, and secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a lithium secondary battery capable of preventing the generation of a dendrite of lithium metal and alloy phase, the pulverization and the like of the electrode for a long period, and improving the energy density, the cycle life and the efficiency. SOLUTION: This negative electrode for the secondary battery has a structure wherein carbon material particles 2a (for example, graphite) capable of storing and releasing lithium ions, oxide particles 3a (for example, silicon oxide, aluminum oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, phosphoric acid compound and boric acid compound) capable of storing and releasing lithium, and particles 4a of metals (for example, silicon, aluminum, tin, indium and zinc) capable of alloying with lithium, are mixed on a collector 1a.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a negative electrode for a secondary battery and a method for manufacturing the same.

[0002]

2. Description of the Related Art A non-aqueous electrolyte lithium secondary battery using a lithium metal or a lithium alloy as a negative electrode is superior to graphite, which is a negative electrode material of a lithium ion secondary battery, in that it has a large energy density and a large electromotive force. can get. However, in the case of lithium metal, dendritic dendrites grow (volume change) on the surface thereof, and the metallic lithium contained in the dendrite is deactivated, causing a problem in battery safety, or There may occur a problem such as deterioration of cycle characteristics. Further, in the case of a lithium alloy, pulverization due to volume change during charging / discharging has become a serious problem of cycle deterioration. Thus, controlling the volume change of the metal and alloy negative electrodes during charge and discharge has been a challenge for these negative electrodes.

Various methods have been proposed as methods for overcoming the problems of the lithium metal and lithium alloy negative electrodes. For example, it has been proposed to suppress the generation of dendrites by providing a film of lithium fluoride or the like on the surface of lithium metal or a lithium alloy by utilizing a chemical reaction.

Japanese Patent Laid-Open No. 7-302617 discloses a technique in which a lithium negative electrode is exposed to an electrolytic solution containing hydrofluoric acid, and the negative electrode is reacted with hydrofluoric acid to cover the surface with a film of lithium fluoride. Is disclosed. Hydrofluoric acid is produced by the reaction of LiPF ₆ and a trace amount of water. On the other hand, a film of lithium hydroxide or lithium oxide is formed on the surface of the lithium negative electrode by natural oxidation in air. The reaction of these forms a film of lithium fluoride on the surface of the negative electrode. However, this lithium fluoride film is formed by utilizing the reaction between the electrode interface and the liquid, and side reaction components are easily mixed in the film, and it is difficult to obtain a uniform film. In addition, there is a case where the lithium hydroxide or lithium oxide film is not formed uniformly or there is a part where the lithium is exposed. In these cases, it is not possible to form a uniform thin film. However, there may be a safety problem due to the reaction of lithium with water or hydrogen fluoride. Further, if the reaction is insufficient, unnecessary films other than the fluorides may remain, and adverse effects such as a decrease in ionic conductivity may be considered. Furthermore, in the method of forming a fluoride layer by utilizing such a chemical reaction at the interface, it is difficult to form a stable film with a high yield because the selection range of usable fluorides and electrolytes is limited. It was

In Japanese Patent Laid-Open No. 8-250108, a mixed gas of argon and hydrogen fluoride is reacted with an aluminum-lithium alloy to obtain a lithium fluoride film on the surface of the negative electrode. However, when a coating is present on the surface of the lithium metal in advance, particularly when a plurality of coatings are present, the reaction is likely to be non-uniform, and it is difficult to form a coating of lithium fluoride uniformly. Therefore, it is difficult to obtain a lithium secondary battery having sufficient cycle characteristics.

Japanese Unexamined Patent Publication (Kokai) No. 11-288706 discloses a surface containing a substance having a rock salt type crystal structure as a main component on the surface of a lithium sheet in which a uniform crystal structure, that is, a (100) crystal plane is preferentially oriented. Techniques for forming a film structure are disclosed. By doing so, it is said that a uniform precipitation dissolution reaction, that is, charging / discharging of the battery can be carried out, dendrite precipitation of lithium metal can be suppressed, and the cycle life of the battery can be improved. It is described that the material used for the surface coating preferably has a lithium halide, and it is preferable to use a solid solution of at least one selected from LiCl, LiBr, and LiI and LiF. Specifically, LiCl, LiBr, L
In order to form a solid solution film of at least one of iI and LiF, it was prepared by pressing (rolling) (10
0) A lithium sheet whose crystal planes are preferentially oriented,
A negative electrode for a non-aqueous electrolyte battery is prepared by immersing it in an electrolytic solution containing at least one of chlorine molecule or chlorine ion, bromine molecule or bromine ion, iodine molecule or iodine ion and fluorine molecule or fluorine ion. In the case of this technology, a rolled lithium metal sheet is used, and since the lithium sheet is easily exposed to the atmosphere, a film derived from water or the like is easily formed on the surface, and the presence of active points becomes non-uniform. It became difficult to form a stable film, and the effect of suppressing Dentrite was not always sufficiently obtained.

Further, oxides such as silicic acid containing lithium are disclosed in JP-A-7-230800, JP-A-7-29602 and JP-A-2000-77075. It is disclosed that the use of an amorphous silicon oxide does not cause crystal collapse and the formation of irreversible substances. However, in the case of the negative electrode using the oxide as it is, it becomes difficult to realize high charge / discharge efficiency due to irreversible capacity. Further, after several hundred cycles, dendrite formation and pulverization may occur.

Further, the above-mentioned conventional techniques have the following common problems. That is, when a film made of a lithium halide or a glassy oxide is formed on a layer made of lithium or an alloy thereof, although the effect of suppressing dendrite can be obtained to some extent in the initial use, when repeatedly used, The film deteriorates and the function as a protective film decreases. This is because the layer made of lithium or its alloy changes its volume by occluding / releasing lithium, while the film made of lithium halide or the like located on the upper side hardly changes its volume. It is considered that the internal stress is generated at the interface. By generating such internal stress,
In particular, it is considered that a part of the film made of lithium halide or the like is damaged and the dendrite suppressing function is deteriorated.

On the other hand, various studies have been conducted on a technique for forming a negative electrode active material layer by using a plurality of different negative electrode materials in combination.

Japanese Unexamined Patent Publication No. 2000-21392 discloses a negative electrode using graphite as a main negative electrode material and an auxiliary negative electrode material having a Li emission potential higher than that of a carbon material than that of a carbon material. As the auxiliary negative electrode material, specifically, a composite oxide containing Sn or Si is disclosed. It is said that the use of such a negative electrode material solves the problem that the negative electrode potential sharply rises at the end of discharge, and improves the deterioration of cycle characteristics and storage characteristics due to overdischarge.

Further, Japanese Patent No. 3055892 discloses that
Disclosed is a negative electrode formed by mixing a conductive auxiliary agent composed of carbon particles supporting a metal capable of forming an alloy with lithium, graphite, and amorphous carbon. If such a configuration is adopted, a metal is interposed between the carbon particles, and it is said that the electrical conductivity can be improved, the charge / discharge speed can be improved, and the discharge capacity can be improved.

However, these do not prevent damage to the negative electrode due to volume change.

[0013]

SUMMARY OF THE INVENTION In view of these circumstances,
An object of the present invention is to provide a negative electrode for a lithium secondary battery, which is capable of preventing dendrite generation of a lithium metal negative electrode, pulverization of an active material, and the like for a long period of time, and which is excellent in energy density, cycle life and efficiency.

[0014]

According to the present invention for solving the above-mentioned problems, (a) carbon material particles capable of occluding and releasing lithium ions, (b) metal particles alloyable with lithium, and (c). Provided is a negative electrode for a secondary battery, which comprises an active material layer containing oxide particles capable of occluding and releasing lithium ions.

The present invention includes the particles (a) to (c) described above. These have different potentials when releasing lithium. That is, in the process of releasing lithium from a battery in a charged state, in order of decreasing emission potential,
Lithium is released in the order of (a), (b), and then (c). When a negative electrode material with a single lithium emission potential is used, a large amount of lithium is released at that potential, causing a rapid volume change and damaging the negative electrode (eg, pulverization of the active material).
Cause to bring. On the other hand, in the present invention,
At the lithium emission potential corresponding to each of the particles (a) to (c), lithium is gradually released, and this problem is improved. Furthermore, in the present invention, (a)
Since all of (c) to (c) are present as particles, it is possible to effectively suppress the occurrence of stress and strain due to volume change. Even if multiple materials with different lithium emission potentials are used, if these materials each form a layer and have a layered structure, the contact between different materials becomes surface contact and remains at the interface of each layer during the charging and discharging process. Stress and residual strain will be generated. On the other hand, when the aggregate of particles is used as in the present invention, the contact between different materials is point contact between particles, so that the generation of residual stress and residual strain can be suppressed to the minimum.

Further, in the present invention, (a) to (c)
Not only do the respective particles of No. 3 differ in the lithium emission potential, but also the change in volume when releasing lithium is different. The volume change is remarkably large in (b) and relatively small in (a) and (c). Therefore, when lithium is released in the above order, the volume change due to the lithium release changes in the order of small, large, and small. In this way, if large volume changes and small volume changes alternately appear in the process of lithium release, residual strain / residual stress of the negative electrode active material layer, etc. can be more effectively reduced, and charge / discharge efficiency and capacity can be reduced. The maintenance rate is improved.

As described above, the negative electrode according to the present invention is
Since the negative electrode is formed by mixing three types of active material particles having different lithium emission potentials and the degree of volume change due to lithium, local stress concentration in the active material layer is eliminated, and battery characteristics, especially cycle characteristics, are reduced. Improvement is achieved. In addition, when the oxide particles (c) include the metal oxide forming the metal particles (b) in the above negative electrode, the transition of the charge / discharge potential becomes smoother, and the residual strain / residual stress becomes more Effectively reduced.

Further, according to the present invention, with respect to the lithium reference potential, (A) particles made of a material having a lithium emission potential of less than 0.3 V, and (B) a material having a lithium emission potential of 0.3 V or more and less than 0.6 V. A negative electrode for a secondary battery is provided, which comprises an active material layer containing the following particles and (C) particles made of a material having a voltage of 0.6 V or more.

According to the present invention, the electrode resistance can be reduced by including particles having a low lithium emission potential of less than 0.3V. In addition, lithium is released stepwise as the potential changes from the low potential to the high potential, and abrupt volume change can be prevented. Therefore, local stress concentration in the active material layer is eliminated, and battery characteristics are improved. The upper limit of the lithium emission potential of the particles (C) is not particularly limited, but may be 1.3 V, for example. In the above invention, as the particles (A), (B) and (C), for example, the above-mentioned (a) carbon material particles capable of absorbing and releasing lithium ions, (b) metal particles capable of alloying with lithium, And (c) oxide particles capable of occluding and releasing lithium ions can be used, and carbon material particles can be used as the particles (A), metal particles can be used as the particles (B), and oxide particles can be used as the particles (C). it can. Further, both particles (B) and (C) may be metal particles or oxide particles.

Further, according to the present invention, there is provided a secondary battery including the above negative electrode. In this secondary battery, generation of dendrites and pulverization of active material are prevented for a long period of time, and excellent cycle characteristics are exhibited.

Further, according to the present invention, (a) carbon material particles capable of occluding and releasing lithium ions, (b) metal particles capable of alloying with lithium and (c) occluding lithium,
And a step of preparing a paste by dissolving or dispersing the releasable oxide particles and a binder in a solvent, and applying the paste on a current collector, followed by drying. A method for producing a negative electrode for a secondary battery is provided.

According to this manufacturing method, each of the particles (a) to (c) is uniformly dispersed in the solvent together with the binder, and as a result, stress or strain is locally generated in the charging / discharging process. And a negative electrode for a secondary battery having excellent cycle characteristics and the like is obtained.

In this production method, (a), (b) and (c) and the binder can be dissolved or dispersed in the solvent substantially simultaneously. In this case, the particles are more evenly dispersed.

Further, according to the present invention, particles made of a material having a lithium emission potential (A) of less than 0.3 V,
A step of dissolving or dispersing (B) particles made of a material of 0.3 V or more and less than 0.6 V and (C) particles made of a material of 0.6 V or more, and a binder in a solvent to prepare a paste. And a step of applying the paste onto a current collector and then drying the paste, and a method for producing a negative electrode for a secondary battery, comprising:

According to this manufacturing method, each of the particles (A) to (C) is uniformly dispersed in the solvent together with the binder, and as a result, stress or strain locally occurs during the charge / discharge process. And a negative electrode for a secondary battery having excellent cycle characteristics and the like is obtained. The upper limit of the lithium emission potential of the particles (C) is not particularly limited, but may be 1.3 V, for example.

In this production method, (A), (B) and (C) and the binder can be dissolved or dispersed in the solvent substantially simultaneously. In this case, the particles are more evenly dispersed.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, particles (a),
The component ratio of each particle to the total of (b) and (c) is not particularly limited, but for example, the particle (a) is 40% by mass or more and 90% by mass or less, and the particle (b) is 5% by mass or more and 50% by mass or more. Hereinafter, it is preferable that the content of the particles (c) is 5% by mass or more and 50% by mass or less.

In the present invention, the particles (A) and (B)
The component ratio of each particle to the total of (C) and (C) is not particularly limited, but, for example, 40% by mass or more of the particles (A) is used.
It is preferable that the content of the particles (B) be 5% by mass or more and 50% by mass or less, and the particles (C) be 5% by mass or more and 50% by mass or less.

In the secondary battery negative electrode according to the present invention, between the particles (a), (b) and (c), or
The particles (A), (B) and (C) may be bound to each other with a binder. In the present invention, since the contact between the particles made of different materials is point contact, it is less likely to bind other particles to each other, for example, in the form in which one particle is carried other particles, The contact area between them becomes large, and the constraint between the particles becomes large. Therefore, the effect of reducing residual stress and residual strain in the active material layer may not be sufficiently obtained.

In the present invention, the oxide particles (c) may be an oxide of the metal forming the metal particles (b). For example, the metal particles (b) can be silicon and the oxide particles (c) can be silicon oxide. In this way, lithium is gradually occluded and released during the charging / discharging process, local volume change of the active material layer is suppressed, and the effect of improving cycle characteristics becomes more remarkable. In particular, when the metal particles (b) and the oxide particles (c) both contain silicon, both high capacity and cycle characteristics can be achieved.
Moreover, when both the metal particles (b) and the oxide particles (c) are made to contain tin, the cycle characteristics are further improved.

In the present invention, the oxide particles (c) may be an oxide of a metal other than the metal forming the metal particles (b). In such a case, depending on the selection of the material, it is possible to achieve both the improvement in capacity and the improvement in cycle characteristics in a well-balanced manner.

In the present invention, the average particle size of the metal particles (b) may be smaller than the average particle size of the carbon material particles (a) and the average particle size of the oxide particles (c). By doing so, the metal particles (b) having a small volume change due to charge / discharge have a relatively small particle diameter, and the carbon material particles (a) and the oxide particles (c) having a large volume change.
Has a relatively large particle size, so that dendrite formation and alloy pulverization are more effectively suppressed. Also, during charging / discharging, lithium particles are occluded and released in the order of large particle size, small particle size, and large particle size. From this point as well, the occurrence of residual stress and residual strain is suppressed. To be done.

In the present invention, the average particle size of the particles (B) may be smaller than the average particle size of the particles (A) and the average particle size of the particles (C). By doing this, particles of large particle size, particles of small particle size,
Lithium is occluded and released in the order of large-diameter particles, so that the occurrence of residual stress and residual strain can be suppressed more effectively. The average particle diameter of the particles (B) is, for example, 20 μm or less, more preferably 15 μm or less.

In the present invention, the lithium metal layer may be provided on the active material layer. By doing so, the irreversible capacity of the carbon material and the oxide material can be eliminated. Especially by forming amorphous lithium film without crystal defects and non-uniformity,
High charging / discharging efficiency can be realized.

In the present invention, the carbon material functions as an active material for each of carbon, oxide and metal, while the carbon material has an effect of reducing electronic conductivity and volume change at the time of a lithium alloy reaction,
The oxide has the effect of relaxing the ionic conductivity and the volume change during alloying. In addition, by mixing carbon, oxide, and metal having different potentials where the charge-discharge reaction occurs, there is an effect of suppressing local volume change due to alloying.

Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of the negative electrode according to the present invention. This negative electrode is formed in a state in which carbon material particles, metal particles, and oxide particles having different particle diameters are uniformly mixed, and a lithium metal film is formed on the surface thereof.

By including a carbon material and an oxide material capable of occluding and releasing lithium ions in the metal phase exhibiting a large volume change due to the charge and discharge reaction of lithium, one of lithium to be occluded and released in the metal phase is included. The part can be occluded and released, thereby reducing the volume change of the metal or alloy. In particular, the carbon material can absorb the strain energy generated in the metal or alloy phase, and can enhance the electron conductivity between particles. Further, the oxide material has an effect as a lithium ion conductor that smoothly moves lithium ions to the metal or alloy phase, and can absorb strain generated in the metal or alloy phase. As a result, dendrite precipitation in the metal phase and pulverization of the alloy phase can be prevented.

The carbon material having the smallest volume change during charging / discharging has the largest particle size, and the second smallest particle size is an oxide, and the smallest particle size of the metal capable of forming an alloy with lithium having the largest volume change. Also more effectively prevents dendrite formation and alloy pulverization.

By uniformly mixing an oxide which has a particle size smaller than that of carbon particles and a lithium which has a particle size smaller than that of an oxide and a metal which can be alloyed with each other, the volume change in the metal or alloy phase can be more effectively reduced. it can.

Furthermore, by mixing carbon, oxide, and metal having different potentials for charge / discharge reaction, it is possible to suppress a rapid volume change in the metal or alloy phase.

As the carbon material, graphite that occludes lithium, amorphous carbon, diamond-like carbon, carbon nanotubes, or the like, or a composite thereof can be used, and among these, a graphite material is particularly preferable. Graphite materials have high electron conductivity, excellent adhesion to current collectors made of metals such as copper, and excellent voltage flatness, and are formed at higher processing temperatures than amorphous materials, etc. Is less, and it works advantageously for improving the negative electrode performance.

The metal forming an alloy with lithium metal is, for example, Al, Si, Pb, Sn, In, Bi, Ag, B.
It is composed of a binary or ternary or more alloy with a, Ca, Hg, Pd, Pt, Te, Zn, La and the like. As the lithium alloy, an amorphous alloy is particularly preferable.
This is because the amorphous structure hardly causes deterioration due to nonuniformity such as grain boundaries and defects.

As the oxide, any one of silicon oxide, aluminum oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, phosphoric acid, boric acid, or a mixture thereof may be used. In particular, silicon oxide is used. It is preferable to include. The structure is preferably in an amorphous state. This is because silicon oxide is stable and does not cause a reaction with other compounds, and the amorphous structure does not lead to deterioration due to nonuniformity such as grain boundaries and defects. As the film forming method, vapor deposition method, CVD
A method such as a sputtering method or a sputtering method can be used.

The lithium metal formed on the surface of the negative electrode is
Sites that generate irreversible capacity of carbon materials and oxide materials can be eliminated. This can prevent a decrease in charge / discharge efficiency. Amorphous lithium metal is particularly preferable. This is because the amorphous structure hardly causes deterioration due to nonuniformity such as grain boundaries and defects.

In the negative electrode of the present invention, by combining a carbon material, an alloy material and an oxide material having different redox potentials, a flat charge / discharge curve can be obtained and the volume change during charge / discharge can be reduced. As described above, it is preferable that both the oxide material and the carbon material are present, but only one of them may be used. Further, the lithium metal preferably covers the entire surface of the negative electrode, but may have a form of covering a part thereof. The lithium metal is preferably formed in contact with the surface of the negative electrode. By doing so, the effect of reducing the irreversible capacity of the oxide or carbon material becomes large.

The particle size of the oxide is 1 / the particle size of graphite.
3 or less, the particle size of the metal forming an alloy with lithium,
It is preferable that the particle size be 1/2 or less of the particle size of the oxide. If the particle size is controlled in this way, a volume expansion relaxation effect of the metal and alloy phases can be sufficiently obtained, and a secondary battery having an excellent balance of energy density, cycle life and efficiency can be obtained.

The carbon material and the oxide are contained in an amount of 20% to 80% in either or mixed form. In a lithium alloy, the proportion of lithium in the alloy changes with charge / discharge reaction to a minimum of 10% and a maximum of 90%.

Lithium metal should be formed by an appropriate method such as a melt cooling method, a liquid quenching method, an atomizing method, a vacuum evaporation method, a sputtering method, a plasma CVD method, a photo CVD method, a thermal CVD method, a sol-gel method. You can Alternatively, lithium metal may be laminated on the surface of the negative electrode and melted to form a film.

The negative electrode according to the present invention is excellent in flexibility with respect to volume changes of metals and alloy phases, uniformity of ion distribution, and physical / chemical stability. As a result, dendrite generation and lithium pulverization can be effectively prevented, and cycle efficiency and life are improved. Further, since the irreversible capacity site contained in the carbon material and the oxide material is eliminated by the lithium metal deposited on the surface, the charge / discharge efficiency does not decrease.

Used in the lithium secondary battery of the present invention
As a positive electrode that can be used, it can store and release lithium
Various materials such as Li_xMO_Two(However, M is small
At least one transition metal is represented. ) Etc. complex oxides, ingredients
Physically, Li_xCoO_Two, Li_xNiO_Two, Li_xM
n_TwoO_Four, Li_xMnO_Three, Li_xNi_yC_1-yO _Two
Or organic sulfur compounds, conductive polymers, etc.
Carbon black or other conductive material, PVDF or other binder
Dispersion with solvents such as N-methyl-2-pyrrolidone (NMP)
If the kneaded material is applied to a substrate such as aluminum foil,
Can be used.

In the lithium secondary battery according to the present invention, in a dry air or inert gas atmosphere, the negative electrode and the positive electrode are laminated via a separator, or the laminated product is wound and then housed in a battery can or A battery can be manufactured by sealing with a flexible film or the like made of a laminate of a synthetic resin and a metal foil. As the separator, a polyolefin such as polypropylene or polyethylene, or a porous film such as a fluororesin is used.

The electrolyte used in the present invention is propylene.
Carbonate (PC), ethylene carbonate (E
C), butylene carbonate (BC), vinylene carbo
Cyclic carbonates such as nate (VC), dimethyl car
Bonate (DMC), diethyl carbonate (DE
C), ethyl methyl carbonate (EMC), dipropy
Chain carbonates such as carbonate (DPC), gui
Aliphatics such as methyl acidate, methyl acetate, ethyl propionate
Γ-La, such as carboxylic acid esters and γ-butyrolactone
Ketones, 1,2-ethoxyethane (DEE), Etoki
Chain ethers such as simethoxyethane (EME), TET
Rings such as lahydrofuran and 2-methyltetrahydrofuran
Ethers, dimethyl sulfoxide, 1,3-diox
Solan, formamide, acetamide, dimethylform
Amide, dioxolane, acetonitrile, propylnit
Lil, nitromethane, ethyl monoglyme, triphosphate
Ester, trimethoxymethane, dioxolane derivative,
Sulfolane, methylsulfolane, 1,3-dimethyl-2
-Imidazolidinone, 3-methyl-2-oxazolidino
Amine, propylene carbonate derivative, tetrahydrofuran
Derivative, ethyl ether, 1,3-propanesalt
, Anisole, N-methylpyrrolidone, fluorinated calcium
One kind of aprotic organic solvent such as borate ester or
Mix and use two or more types and dissolve in these organic solvents.
Dissolve the lithium salt. As a lithium salt, for example
If LiPF₆, LiAsF₆, LiAlCl_Four, LiC
10_Four, LiBF_Four, LiSbF₆, LiCF_ThreeS
O_Three, LiC_FourF₉CO_Three, LiC (CF_ThreeS
O_Two)_Two, LiN (CF_ThreeSO_Two)_Two, LiN (C_TwoF
₅SO_Two)_Two, LiB ₁₀Cl₁₀, Lower aliphatic carbo
Lithium carboxylate, Lithium chloroborane,
Lithium phenyl borate, LiBr, LiI, LiSC
Examples thereof include N, LiCl, and imides. Also electrolysis
A polymer electrolyte may be used instead of the liquid.

The secondary battery according to the present invention has a structure as shown in FIG. 2, for example. FIG. 2 is a schematic enlarged cross-sectional view in the thickness direction of the negative electrode current collector of the secondary battery according to the present invention. The positive electrode is formed by forming a layer 12 containing a positive electrode active material on the positive electrode current collector 11. The negative electrode is formed by forming a layer 13 containing a negative electrode active material on a negative electrode current collector 14. The positive electrode and the negative electrode are arranged so as to face each other with the electrolytic solution 15 and the porous separator 16 in the electrolytic solution 15 interposed therebetween. The porous separator 16 is arranged substantially parallel to the layer 13 containing the negative electrode active material.

The shape of the secondary battery according to the present invention is not particularly limited, but examples thereof include a cylindrical shape, a square shape, and a coin shape.

[0056]

EXAMPLES (Example 1) (Production of negative electrode and charge / discharge curve) Production of the negative electrode of Example 1 will be described. For the structure of the battery, refer to FIG. In this embodiment, the negative electrode current collector 1a is a copper foil, the carbon material particles 2a are graphite having an average particle size of 40 μm, and the oxide particles 3a.
Is a silicon oxide (SiO _x ) with an average particle diameter of 13 μm (0 <x ≦
2) The metal particles 4a were silicon having an average particle size of 6 μm, and the lithium metal layer 5a was a lithium metal layer having a thickness of 0.2 μm. As the copper foil of the negative electrode current collector 1a, an electrolytic copper foil having a thickness of 10 μm was used. The carbon material particles 2a, the oxide particles 3a, and the metal particles 4a were mixed with polyvinylidene fluoride at a mass ratio of 20:40:40 and dispersed and kneaded with N-methyl-2-pyrrolidone as a solvent to form a copper foil 1a. It was formed by applying, drying and compressing. The lithium metal layer 5a layer was produced by the vacuum evaporation method. The degree of vacuum in the vacuum vapor deposition device is 10
^{Reduce the} pressure to ^-6 to 10 ^-5 Pa and roll to a width of 60 mm.
It was deposited by electron beam or resistance heating. The negative electrode of this example was formed by such a method. The capacity of the prepared negative electrode is the sum of the capacity of graphite (372 mA / kg), the capacity of lithium-silicon alloy (1440 mA / kg), and the capacity of silicon oxide (1200 mA / kg).

FIG. 3 shows a charge / discharge curve obtained by producing a coin cell using this negative electrode and lithium metal as a counter electrode.
It can be seen that a large capacity exceeding 1000 mAh / g is obtained, the potential flatness is good, and the efficiency is high. It is considered that the potential flatness is good because the particles are uniformly dispersed and the adhesion between the particles is high. Further, it can be seen that the charge / discharge efficiency is extremely increased by forming a film of lithium metal on the surface.

Next, as a control experiment, the following 2 was carried out in the same manner as above except that the particles constituting the active material layer were changed.
Various types of cells were prepared and the charge / discharge behavior was evaluated.

First, except for the metal particles 4a, carbon material particles 2a (graphite) and oxide particles 3a (silicon oxide).
To form an active material layer, and a lithium metal layer 5a was provided thereon to prepare a negative electrode. The mass ratio of SiO and graphite is 10:90.
And N-methyl-2 containing polyvinylidene fluoride
-Slurry was prepared by dispersing in pyrrolidone solution. The slurry was applied onto a copper foil, dried and compressed to form a negative electrode. A coin-type cell was constructed for this negative electrode in the same manner as described above, and the charge / discharge behavior was evaluated. The results are shown in FIG. The voltage is generally higher than that in FIG. It is considered that this is because the resistance of the negative electrode increased. For this reason, the usable region where the operating voltage is above a certain level is narrowed, and the substantial battery capacity is reduced from this point as well.

Further, except for the carbon material particles 2a, silicon oxide is used as the oxide particles 3a and Pb-S is used as the metal particles 4a.
An n-alloy was used to form an active material layer, and a lithium metal layer 5a was provided thereon to prepare a negative electrode. The mass ratio of Pb-Sn alloy and SiO was set to 55: 40: 5. A coin type cell was constructed in the same manner as described above, and the charge / discharge behavior was evaluated. The result is shown in FIG. In FIG. 5, the plateau corresponding to the lithium discharge potential of each particle is clearly shown. In a state corresponding to this plateau, lithium is occluded and released in specific particles, so that a volume change locally occurs, which causes dendrite or active material to be finely divided. Further, in the charge / discharge curve of FIG. 5, the voltage is generally higher and the battery capacity is decreased as compared with FIG. In addition, since the region on the left side of the drawing has a particularly high potential, the usable region where the operating voltage is above a certain level is narrowed, and from this point as well, the substantial battery capacity is reduced.

(Production of Battery) Using this negative electrode and LiMn ₂ O ₄ as a positive electrode, a mixed solvent of ethylene carbonate and diethyl carbonate was used as a solvent, and 1 mol / L was added to this solvent.
And an electrolyte solution by dissolving LiPF ₆ in. Then, the negative electrode and the positive electrode were laminated with a separator interposed therebetween to produce a coin-type secondary battery.

(Charge / Discharge Cycle Test) At a temperature of 20 ° C., the charge rate was 0.01 C, the discharge rate was 0.02 C, the charge end voltage was 4.2 V, and the discharge end voltage was 3.0 V. Capacity retention rate (%) is the discharge capacity (mA) after 100 cycles.
It is a value obtained by dividing h) by the discharge capacity (mAh) at the 10th cycle. The results obtained in the cycle test are shown in the table below.

The initial charge / discharge efficiency and capacity retention in Example 1 are much higher than those in Comparative Example 1. In particular, it can be seen that the improvement of the initial charge / discharge efficiency is considerably increased by forming the lithium metal film.
Further, it is considered that the increase in the capacity retention rate was due to the volume change due to charge / discharge being sufficiently suppressed by the graphite layer and the oxide layer.

[0064]

[Table 1]

[0065]

[Table 2]

(Examples 2 to 7) Instead of the structure shown in Example 1, a negative electrode was made of the materials shown in the above table, and a negative electrode and a battery were prepared and evaluated in the same manner as in Example 1. From the results shown in the following table, the batteries shown in the examples have improved initial charge and discharge efficiency and improved capacity retention rate, that is, cycle characteristics as compared with Comparative Example 1 and Comparative Examples 2 to 5. It was confirmed that it was improved.

(Examples 8 to 14) Negative electrodes without the lithium metal layer 5a shown in Examples 1 to 7 were prepared and evaluated in the same manner as in Example 1. The evaluation results are shown in the table below. It can be seen that the capacity retention ratio is higher than those of Comparative Examples 1 to 10. These results also show that the effects of graphite and oxides suppress the dendrite formation and pulverization of the metal and alloy phases. However, when the lithium metal was not formed on the surface, the initial charge / discharge efficiency was reduced as compared with Examples 1-7. This is probably due to the irreversible capacity of graphite and oxide.

[0068]

[Table 3]

[0069]

[Table 4]

Comparative Example 1 In this comparative example, silicon (metal particles 4a) was used as the negative electrode, and a negative electrode not forming the carbon material particles 2a, oxide particles 3a and lithium metal layer 5a was used. Make a battery similar to 1.
The results of examining the cycle characteristics as in Example 1 are shown in the table below.

(Comparative Examples 2 to 7) A battery was prepared in the same manner as in Example 1 except that the negative electrode was made of the materials shown in the table, and the cycle characteristics were examined in the same manner as in Example 1. The results are shown in the table below.

It can be seen that when the lithium metal is formed on the surface, the initial charge / discharge efficiency is high, and in the case where either graphite or oxide is present, the capacity retention rate is high. This indicates that even if either graphite or oxide is present, it has the effect of suppressing the volume change of the metal or alloy phase. However, it is shown to be inferior to the effect in the case where both graphite and oxide are present.

[0073]

[Table 5]

[0074]

[Table 6]

The lithium emission potentials of the electrode materials shown in Tables 1 to 6 are all less than 0.3V for the carbon material particles 2a and 0.3V or more for the metal particles 4a with lithium as the reference potential. Less than 0.6V, oxide particles 3a 0.6V
That is all.

[0076]

According to the present invention, a lithium secondary battery having excellent characteristics such as energy density and electromotive force obtained when lithium metal or a lithium alloy is used as a negative electrode and having excellent cycle life and safety is provided. Can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a negative electrode portion of a lithium secondary battery used in Example 1 of the present invention.

FIG. 2 is a schematic configuration diagram of a secondary battery according to the present invention.

FIG. 3 is a charge / discharge curve diagram of the negative electrode according to the present invention.

FIG. 4 is a charge / discharge curve diagram of a conventional negative electrode.

FIG. 5 is a charge / discharge curve diagram of a conventional negative electrode.

[Explanation of symbols]

1a Negative electrode current collector 2a Carbon material particles 3a oxide particles 4a metal particles 5a lithium metal layer 11 Positive electrode current collector 12 Layer containing positive electrode active material 13 Layer containing negative electrode active material 14 Negative electrode current collector 15 Electrolyte solution of electrolyte aqueous solution 16 Porous separator

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroki Yamamoto             5-7 Shiba, Minato-ku, Tokyo NEC Corporation             Inside the company (72) Inventor Jiro Iriyama             5-7 Shiba, Minato-ku, Tokyo NEC Corporation             Inside the company (72) Inventor Tamaki Miura             5-7 Shiba, Minato-ku, Tokyo NEC Corporation             Inside the company (72) Inventor Mariko Miyaji             5-7 Shiba, Minato-ku, Tokyo NEC Corporation             Inside the company F term (reference) 5H029 AJ03 AJ05 AK03 AK05 AK16                       AL02 AL06 AL07 AL11 AL12                       AM03 AM04 AM05 AM07 CJ02                       CJ22 DJ16 DJ18 HJ18                 5H050 AA07 AA08 BA17 CA02 CA07                       CA08 CA09 CA11 CA20 CB02                       CB07 CB08 CB11 CB12 DA03                       FA17 FA18 FA19 FA20 GA02                       GA22 HA18

Claims (21)

[Claims] 1. An active material containing (a) carbon material particles capable of storing and releasing lithium ions, (b) metal particles capable of alloying with lithium, and (c) oxide particles capable of storing and releasing lithium ions. A negative electrode for a secondary battery, comprising a layer. 2. The secondary battery negative electrode according to claim 1, wherein the particles (a), (b) and (c) are bound together by a binder. Negative electrode for secondary battery. 3. The negative electrode for a secondary battery according to claim 1, wherein the oxide particles (c) are silicon oxide.
A secondary battery containing one or more compounds selected from the group consisting of aluminum oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, phosphoric acid and boric acid, or an alloy of the compound and lithium. Negative electrode. 4. The negative electrode for a secondary battery according to claim 1, wherein the oxide particles (c) have an amorphous structure. 5. The negative electrode for a secondary battery according to claim 1, wherein the metal particles (b) are silicon,
A negative electrode for a secondary battery, comprising one or more metals selected from the group consisting of aluminum, tin, indium and zinc, or an alloy of the metals and lithium. 6. The negative electrode for a secondary battery according to claim 1, wherein the oxide particles (c) are oxides of the metal forming the metal particles (b). Negative electrode for secondary battery. 7. The secondary battery negative electrode according to claim 1, wherein the oxide particles (c) are oxides of metals other than the metal forming the metal particles (b). And a negative electrode for a secondary battery. 8. The negative electrode for a secondary battery according to claim 1, wherein the carbon material particles (a) are made of graphite. 9. The negative electrode for a secondary battery according to claim 1, wherein a lithium metal layer is provided on the active material layer. 10. The negative electrode for a secondary battery according to claim 1, wherein the average particle size of the metal particles (b) is
A negative electrode for a secondary battery, which is smaller than the average particle diameter of the carbon material particles (a) and the average particle diameter of the oxide particles (c). 11. The secondary battery negative electrode according to claim 1, wherein the metal particles (b) and the oxide particles (c) both contain silicon. Negative electrode. 12. The secondary battery negative electrode according to claim 1, wherein the metal particles (b) and the oxide particles (c) both contain tin. Negative electrode. 13. A lithium emission potential with respect to a lithium reference potential, (A) particles made of a material of less than 0.3 V, (B) particles made of a material of 0.3 V or more and less than 0.6 V, and (C) A negative electrode for a secondary battery, comprising an active material layer containing particles made of a material having a voltage of 0.6 V or more. 14. The negative electrode for a secondary battery according to claim 13, wherein the particles (A), (B) and (C) are bound together by a binder. Negative electrode for secondary battery. 15. The negative electrode for a secondary battery according to claim 13 or 14, wherein a lithium metal layer is provided on the active material layer. 16. The negative electrode for a secondary battery according to claim 13, wherein the particles (B) have an average particle size of
A negative electrode for a secondary battery, which is smaller than the average particle diameter of the particles (A) and the average particle diameter of the particles (C). 17. A secondary battery comprising the negative electrode for a secondary battery according to claim 1. 18. (a) Carbon material particles capable of storing and releasing lithium ions, (b) metal particles capable of alloying with lithium, (c) oxide particles capable of storing and releasing lithium, and a binder. And a step of preparing a paste by dissolving or dispersing in a solvent, and after applying the paste on a current collector,
And a step of drying the negative electrode for a secondary battery. 19. The method for producing a negative electrode for a secondary battery according to claim 18, wherein the particles (a), (b) and (c) and the binder are substantially simultaneously dissolved in a solvent. Alternatively, a method for producing a negative electrode for a secondary battery, which comprises dispersing. 20. The lithium emission potential is (A) 0.3 V.
Particles made of a material of less than (B) 0.3 V or more and 0.
Particles made of material that is less than 6V and (C) 0.6V
The method includes: a step of dissolving or dispersing particles made of the above materials and a binder in a solvent to prepare a paste; and a step of applying the paste on a current collector and then drying the paste. And a method for manufacturing a negative electrode for a secondary battery. 21. The method for producing a negative electrode for a secondary battery according to claim 20, wherein the particles (A), (B) and (C) and the binder are dissolved in a solvent substantially simultaneously. Alternatively, a method for producing a negative electrode for a secondary battery, which comprises dispersing.