JP2003308831A - Nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery having high energy density, wherein expansion and contraction of an electrode does not grow even if a charge/discharge cycle is repeated, a conductive network in the inside of the electrode is not broken, and battery capacity does not decrease and internal resistance does not increase. <P>SOLUTION: This nonaqueous secondary battery is provided with a positive electrode, a negative electrode, and a nonaqueous electrolyte, and it uses an electrode formed by filling a negative electrode material containing a complex comprising a material containing an element capable of forming an alloy with lithium and a conductive material in a collector having a three dimensional structure, as the negative electrode. The negative electrode is formed by filling the negative material in the collector together with a binder and by pressing it. The thickness of the negative electrode is 0.1-10 mm, and its porosity is 20-50%, in this nonaqueous secondary battery. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery having high capacity and excellent cycle characteristics.

[0002]

2. Description of the Related Art Batteries using an alkali metal as an active material are attracting attention as high-performance batteries having a high energy density. Among them, lithium batteries have a particularly high energy density and are excellent in reliability such as storability, so that they are already widely used as power sources for small electronic devices as primary batteries. In addition, recently, with the spread of small portable electric devices, the demand for lithium secondary batteries that can be charged and used repeatedly is rapidly increasing.

As the negative electrode material of this lithium secondary battery, for example, a lithium metal, a lithium alloy, or a carbonaceous material in which lithium is occluded in a carbon material capable of occluding and releasing lithium is used.

A non-aqueous electrolyte secondary battery using a lithium metal or a lithium alloy as a negative electrode can obtain a battery having a high energy density, but as the charge / discharge cycle progresses, dissolution and precipitation of lithium are repeated, and at that time. Since the deposited active lithium reacts with the solvent of the electrolytic solution, chargeable / dischargeable lithium is lost and the charge / discharge efficiency of the negative electrode is reduced. Furthermore, lithium is a dendrite (dendritic crystal).
As a result, the dendrite may penetrate the separator and cause an internal short circuit.

Therefore, in place of lithium metal or lithium alloy, coke or amorphous carbon such as glassy carbon capable of doping and dedoping lithium ions, or carbon material such as natural or artificial graphite is used as the negative electrode. It is used as a material. For example, JP-A-1-204361, JP-A-2-66856, and JP-A-4-248.
No. 31, JP-A-5-17669, etc. describe that this carbon material is used as a negative electrode material to impart cycle durability to a lithium secondary battery.

However, the theoretical capacity of a negative electrode using the above carbon material as a negative electrode material is, for example, 372 mAh for graphite.
/ G, which is insufficient for the recent demand for higher capacity batteries for portable devices. Therefore, recently, silicon (Si) and tin (S), which are elements capable of forming an alloy with lithium, have been developed.
Negative electrode materials such as n) have attracted attention. For example,
Japanese Patent Laid-Open No. 7-29602 discloses that Li _x Si (0 ≦ x
A non-aqueous electrolyte secondary battery using <5) as a negative electrode active material is described.

[0007]

However, although the negative electrode material composed of an element capable of forming an alloy with lithium can have a higher capacity than the carbon material as described above, There is a problem that the negative electrode material expands and contracts greatly, which destroys the conductive network in the negative electrode, significantly lowering the capacity and increasing the internal resistance. Further, in the negative electrode prepared by the conventional method of applying the negative electrode mixture to the metal foil, the negative electrode material greatly expands and contracts, so that the negative electrode itself greatly expands in the thickness direction and the current collecting performance of the current collector deteriorates. Or the negative electrode itself is curved,
Or, a problem that the battery can swells occurs.

Here, the reason why the negative electrode material made of an element capable of forming an alloy with lithium has a large expansion and contraction will be described by taking silicon as an example.

Silicon is a crystallographic unit cell (cubic
Crystal, space group Fd-3m) contains 8 Si atoms
It Unit calculated from lattice constant a = 0.5431 nm
Lattice volume is 0.1592 nm³And one Si atom
Volume occupied (unit cell volume is the number of Si atoms in the unit cell)
Value divided by 0.0199 nm³Is. From silicon
Charge the negative electrode to 100 mV or less (insert lithium
And a lithium-rich compound Li₁₅S
i_FourAnd Li_{twenty one}Si_FiveAnd its capacity is about 4000 mAh
/ G, but the volume expansion coefficient becomes extremely large. An example
For example, Li_{twenty one}Si _FiveUnit cell (cubic crystal, space group F4-
3m) contains 83 Si atoms. The grid
Unit cell volume calculated from the constant a = 1.8750 nm
Is 6.5918 nm³And a body occupied by one Si atom
Product is 0.079 nm³Is. This value is the body of elemental silicon
3.95 times the product. That is, silicon is
The volume increases about 4 times. Furthermore, when charging and discharging like this
Since the volume difference between the two is extremely large, a large strain is generated in the silicon particles.
And the particles are pulverized to create spaces between the particles,
The sexual network is disrupted and can participate in electrochemical reactions.
This will increase the number of areas that cannot be charged and reduce the charge / discharge capacity.
It

On the other hand, Japanese Patent Laid-Open No. 2000-272911 describes a lithium battery having excellent charge / discharge characteristics, which uses composite particles in which silicon particles are embedded in graphite and amorphous carbon as a negative electrode. ing. By compounding graphite and amorphous carbon with silicon, the expansion of silicon particles can be relaxed and the charge / discharge cycle characteristics are improved. However, when the utilization rate of silicon that develops a high capacity of about 1000 mAh / g is high, the charge / discharge cycle characteristics are not sufficient and do not reach the level of practical use. It is considered that this is because when the utilization rate of silicon is high, the expansion / contraction of silicon becomes large, and the expansion / contraction of the composite particles also increases accordingly, and the conductive network inside the negative electrode is destroyed. .

The present invention has been made in order to solve the above-mentioned conventional problems, and the expansion and contraction of the electrode does not increase even if the charge and discharge cycle is repeated, and the conductive network inside the electrode is not destroyed. It is an object of the present invention to provide a high energy density non-aqueous electrolyte secondary battery in which the battery capacity does not decrease and the internal resistance does not increase.

[0012]

In order to achieve the above object, a non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, and
A negative electrode material comprising a non-aqueous electrolyte, and a negative electrode containing a composite of a conductive material and a material containing an element capable of forming an alloy with lithium as a current collector having a three-dimensional structure. It is characterized by using a filled electrode.

By using a current collector having a three-dimensional structure, expansion and contraction of the negative electrode does not increase even if charge and discharge cycles are repeated, and the conductive network inside the negative electrode is not destroyed.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode,
A negative electrode and a non-aqueous electrolyte are provided, and as the negative electrode, a current collector having a three-dimensional structure includes a composite of a material containing an element capable of forming an alloy with lithium and a conductive material. An electrode filled with a negative electrode material is used.

Examples of the element capable of forming an alloy with lithium are silicon, silver, gold, zinc, cadmium, aluminum, gallium, indium, thallium, germanium, tin, lead, antimony and bismuth. To be Particularly, silicon, tin, and aluminum are preferable from the viewpoint of material cost and handling.

The material containing an element capable of forming an alloy with lithium may be in any of a crystalline state, a low crystalline state and an amorphous state. Further, as the material, a simple substance of an element capable of forming an alloy with lithium and an alloy or a compound containing those elements can be used. For example, it is a solid solution or an intermetallic compound of silicon, tin, aluminum, silicon oxide (SiO), tin oxide (SnO), silicon, tin, aluminum or the like with another metal. For materials containing silicon and germanium,
For example, it is possible to use an n-type or p-type semiconductor that is significantly reduced in electrical resistance by doping with boron or phosphorus.

Further, these materials containing an element capable of forming an alloy with lithium must be compounded with a conductive material to form a composite. By this composite, it is possible to suppress pulverization of the negative electrode material due to charge / discharge cycles, and it is possible to maintain the conductive network in the negative electrode material particles when pulverized.

The above-mentioned composite is usually in the form of particles, and its average particle diameter is preferably 2 μm or more and 100 μm or less, and particularly preferably 2 to 50 μm. When the average particle size of the composite particles is 2 μm or more, the material containing an element capable of forming an alloy with lithium constituting the composite particles or the conductive material has a particle size of 0.5 μm or more because of its structure. It can be used, granulation and compounding become easy, the specific surface area of the composite particles does not become excessive, and the manufacturing process and battery characteristics are not adversely affected. On the other hand, when the average particle diameter of the composite particles is 50 μm or less, it becomes easy to fill the current collector having a three-dimensional structure, which is advantageous for the production of electrodes.

The content of the element capable of forming an alloy with lithium in the composite is 30% by mass or more,
It is preferably 80% by mass or less. When it is 30 mass% or more,
Individual material particles containing an element capable of forming an alloy with lithium without excessively increasing the utilization rate of the element capable of forming an alloy with lithium when a capacity of about 1000 mAh / g is exhibited. Expansion does not increase,
It becomes difficult to pulverize. Moreover, when it is 80 mass% or less,
Since the number of bonding points between the material containing the element capable of forming an alloy with lithium and the conductive material increases, the construction of the conductive network becomes easy.

As the conductive material contained in the above composite, artificial graphite, natural graphite, earthy graphite, expanded graphite, flake graphite or heat-treated materials thereof, as well as carbon obtained by thermally decomposing organic matter under various conditions. A material or a metal material such as copper can be used. In particular, a fibrous or coiled carbon material or metal material is preferable. Since these are thin threads having a flexible shape, they can effectively follow the expansion and contraction of a material containing an element capable of forming an alloy with lithium which is bonded to or adjacent to them. Because you can. Examples of the fibrous carbon material that can be used in the present invention include polyacrylonitrile (PAN) -based carbon fibers,
There are pitch-based carbon fibers, vapor-grown carbon fibers, and the like, but either may be used.

The method for producing the composite body composed of a material containing an element capable of forming an alloy with lithium and a conductive material is not particularly limited, but for example, the following method can be used. Using silicon as a material containing an element capable of forming an alloy with lithium, when carbon is used as the conductive material, first granulate silicon and carbon,
Then, by a method of carbonizing the carbon precursor by mixing with a carbon precursor such as an organic substance, or a method of carbon coating the surface by a vapor phase method after granulating silicon and carbon, etc. Obtainable. As the granulation method, rolling granulation, compression granulation, sintering granulation, vibration granulation, mixed granulation, crush granulation and the like can be preferably used. The void volume occupancy rate in the composite can be adjusted by controlling the type of mixed material, particle size, mixing ratio, granulation conditions, and the like. As a method of coating carbon by a vapor phase method, a pyrolysis CVD method of thermally decomposing a hydrocarbon-based gas to coat it, a PVD method of vapor deposition by pseudo arc discharge using a carbon rod, and the like can be suitably used.

The composite particles of the present invention obtained as described above preferably have a specific surface area of less than 10 m ² / g. If the specific surface area exceeds 10 m ² / g, the composite particles and the electrolytic solution may react with each other depending on the conditions, and a film may be easily formed on the surface of the composite particles, and lithium may be incorporated into the film for charge / discharge. This is because the irreversible capacity may increase due to an increase in unrelated lithium.

In the negative electrode of the non-aqueous electrolyte secondary battery of the present invention,
A current collector having a three-dimensional structure is filled with a negative electrode material containing the composite particles. That is, since the current collector is integrated with the negative electrode material in a three-dimensionally spread state in the negative electrode material, the conductive network is maintained even if the expansion and contraction of the composite particles is large. Moreover, since the average distance between the negative electrode material and the current collector is small, the internal resistance of the negative electrode is small. Therefore, most of the negative electrode materials exhibit their functions, so that a battery having a large capacity can be obtained and can withstand a large current.

When the current collector is filled with the negative electrode material containing the composite particles, it is preferable to fill the current collector with the binder and press the negative electrode material. The binder can prevent the negative electrode material from falling off, and by pressing at the time of manufacturing the electrode, a contracting force can be applied to the expansion of the electrode in the thickness direction. Therefore, the expansion of the electrode can be suppressed even if the expansion and contraction of the composite particles are large.

The current collector having the three-dimensional structure is preferably a sheet or a mat made of a foamed metal or a fibrous metal sintered body. This is because these are excellent in current collecting performance and have great resistance to expansion and contraction of the negative electrode material.

Hereinafter, the case where silicon is used as a material containing an element capable of forming an alloy with lithium and carbon is used as a conductive material (silicon / carbon composite material) will be described as an example. Will be further explained.

For the negative electrode, for example, a solvent is mixed with a silicon / carbon composite material and a binder made of a fluororesin to prepare a slurry, and the slurry is applied to a foamed metal sheet or a mat of a fibrous metal sintered body. It can be obtained by drying after processing. Then, it is compressed with a press or the like to adjust the thickness and the porosity. Further, the fluororesin and the cross-linking agent are toluene,
It is dissolved in an organic solvent such as xylene, and a powder of a silicon / carbon composite material is mixed with this to make a slurry, which is applied to a foam metal sheet or a mat of fibrous metal sintered body, Remove the solvent by drying at 100 ℃
You may compress and harden it with a press etc., heating at -180 degreeC.

In the negative electrode, since the foamed metal or fibrous metal sintered body and the binder bind the negative electrode material, the silicon / carbon composite material may repeatedly expand and contract as the charge / discharge cycle progresses. However, the contact between the particles of the silicon / carbon composite material is maintained, the increase in the internal resistance of the negative electrode is suppressed, and the initial capacity of the battery can be maintained without the conductive network collapsing.

Since the negative electrode can be compressed with a press or the like at a pressure of preferably 9.8 to 980 MPa to adjust the porosity, the capacity per volume of the negative electrode can be increased. In addition, since an appropriate amount of gap can be secured in the negative electrode to allow the electrolytic solution to be easily impregnated into the negative electrode, and a route necessary for diffusion of lithium ions can be secured, the negative electrode active even when a large current is passed. High utilization rate of substances. Further, even if the composite particles expand during charging, the voids can make up for the particle expansion volume, so that the expansion of the electrode can be suppressed.

As described above, the thickness and porosity of the negative electrode are adjusted by compressing a foamed metal or fibrous metal sintered body filled with a silicon / carbon composite material containing a binder with a press or the like. , Its thickness is preferably 0.1 mm or more,
More preferably, it is 0.15 mm or more. Thickness is 0.1
When it is less than mm, the amount of electrode material carried is small and the battery capacity is small. Further, if it is too thick, it is difficult to adjust the porosity by compression. In this case, if the material is pressed while being heated to the melting point of the binder or higher, the strength of the negative electrode is increased and the battery characteristics are remarkably improved. Further, if the porosity is small, impregnation with the electrolytic solution becomes difficult, the ionic conductivity via the electrolytic solution decreases, the function of the negative electrode material is limited, and the battery capacity decreases, so that the porosity is 20 to 50%. Preferably 25 to 4
It is preferably 0%. The porosity is represented by (volume occupied by voids) / (apparent volume) × 100, and the volume occupied by voids is measured by the mercury porosimetry.

The foamed metal is preferably a spongy porous body having continuous openings. As a result, the internal resistance becomes small, and the conductive network is maintained even after repeated charge and discharge cycles, so that the internal resistance can be prevented from increasing and the expansion of the electrode can be suppressed. Further, the open pore diameter of the foam metal is preferably 10 μm to 1.0 mm. When the opening diameter is 10 μm or more, the mixture of the silicon / carbon composite material and the binder can be easily filled into the opening, and when the opening diameter is 1.0 mm or less, the foamed metal and the negative electrode as the current collector. The average distance between the material and the silicon / carbon composite material in which lithium is occluded does not become large, which makes it easier to maintain the conductive network with charge / discharge cycles, resulting in reduced capacity and increased internal resistance of the electrode. It will not cause.

The porosity of the foam metal is 70 to 99.
% Is preferred. When the open area ratio is 70% or more,
A large amount of the negative electrode material composed of the silicon / carbon composite material and the binder that can be filled in the openings can be filled, and the capacity of the battery can be sufficiently secured. Further, when the porosity is 99% or less, the strength of the foamed metal does not decrease and the force for binding the negative electrode material can be maintained.

For the same reason as in the case of the opening diameter of the foamed metal, the fiber diameter (diameter) of the fibrous metal sintered body is 1 to
It is preferably 50 μm. As the fibrous metal sintered body, a sintered body of short fibers or long fibers is used. The porosity is 50 to 50 for the same reason as that of the foamed metal.
It is preferable to use 95%.

The material of the foamed metal or fibrous metal sintered body used for the negative electrode of the present invention is a metal having corrosion resistance to lithium such as nickel, copper, nickel-copper alloy, nickel-iron-chromium alloy. Is preferably used.

A composite of a material containing an element capable of forming an alloy with lithium and a conductive material can be mixed with a binder to form a mixture for the negative electrode. May be mixed. The conductive material for the negative electrode when producing the mixture is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the constructed non-aqueous electrolyte secondary battery. Usually, natural graphite (scaly graphite, flake graphite, earth graphite, etc.), artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder (copper powder, nickel powder, aluminum powder, silver powder, etc.), A metal fiber or a conductive material such as a polyphenylene derivative described in JP-A-59-20971 can be used. These conductive materials can be used alone, or a plurality of conductive materials can be mixed and used.

As the binder, either a thermoplastic resin or a thermosetting resin may be used. The binder is usually starch, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl pyrrolidone, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),
Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPD
M, styrene-butadiene rubber, butadiene rubber, polybutadiene, fluororubber, polyethylene oxide, and other polysaccharides, thermoplastic resins, polymers having rubber elasticity, and the like, and at least one of these modified substances or a mixture thereof. You can In particular, it is preferable to use a fluororesin that does not dissolve in the solvent of the electrolytic solution and is stable under the condition that the non-aqueous electrolyte secondary battery functions electrochemically. The fluororesin has excellent heat resistance and chemical resistance, and when the fluororesin is used as a binder, the effects of maintaining contact between the negative electrode material particles and preventing the negative electrode material from falling off from the current collector are improved. The fluororesin used for the binder is preferably one that is dispersed or soluble in an organic solvent, such as polytetrafluoroethylene or polyvinylidene fluoride. In this case, it is preferable to disperse or dissolve the binder in an organic solvent, mix this with the negative electrode material to form a slurry, and fill the current collector with the slurry. As the fluororesin, those used together with a curing agent (such as a crosslinking agent) can be preferably used.

The positive electrode of the non-aqueous electrolyte secondary battery of the present invention comprises:
An electrode formed by a conventional coating method can be used.
Furthermore, aluminum, titanium, stainless steel (S
(US316 or SUS316L) as a main component, a foamed metal or fibrous metal sintered body is filled with a mixture of a positive electrode material capable of occluding / releasing lithium and a conductive material together with a binder, and the thickness thereof is 0.1 mm or more. And the porosity is 20-5
You may use what is 0%.

The positive electrode material capable of inserting and extracting lithium includes, for example, 4th group, 5th group, 6th group, 7th group and 8th group of the periodic table.
Chalcogenides such as oxides, complex oxides, sulfides, and the like containing metals belonging to the genus, 9th group, 10th group, 11th group, 12th group, 13th group and 14th group, and oxyhalogens mainly containing these metals Compounds are used. Also, polyaniline,
A conductive polymer material such as polypyrrole, polythiophene, polyacene, polyparaphenylene, or a derivative thereof can also be used as the positive electrode material.

The energy density of the battery can be increased by using a positive electrode material having a high operating potential and a large capacity for occluding / releasing lithium. Therefore, the chemical formula is LiCoO 2.
_It is preferable to use a spinel type lithium manganese composite oxide represented by ₂ , LiNiO ₂ , LiMnO ₂ or LiMn ₂ O ₄ as the positive electrode material.

The particle size of the powder of the positive electrode material is preferably 1 to 80 μm so that an electrode can be easily manufactured, lithium can be occluded and desorbed smoothly, and the volume of the positive electrode material does not become too bulky.

The positive electrode is manufactured, for example, as follows. That is, a mixture of a powder of a positive electrode material, a conductive material and a fluororesin which is a binder is mixed with an organic solvent to form a slurry, and the slurry is applied onto a metal foil, or a foamed metal sheet or a fibrous metal baking is applied. It is applied to a mat of ties and dried to remove the organic solvent. Then, it is compressed by a press or the like to adjust the thickness and porosity of the positive electrode.

As the binder for the positive electrode, the same binder as that used for the negative electrode can be preferably used.

The non-aqueous electrolyte used in the present invention is
Either a non-aqueous liquid electrolyte or a polymer electrolyte can be used, but since a liquid electrolyte generally called an electrolytic solution is often used, the expression "electrolytic solution" will be described below with respect to this liquid electrolyte. That is, the non-aqueous electrolyte solution is composed of an organic solvent and a lithium salt dissolved in the organic solvent. Examples of the organic solvent include propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3. -Dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2
-Oxazolidinone, propylene carbonate derivative,
Tetrahydrofuran derivative, diethyl ether, 1,3
-One of aprotic organic solvents such as propane sultone
A solvent which is a mixture of two or more species can be used.
Further, as the lithium salt to be dissolved in the organic solvent,
For example, LiClO ₄ , LiBF ₆ , LiPF ₆ , LiC
_{F 3 SO 3, LiCF 3 CO} 2, LiAsF 6, LiSb
One or more salts of F ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, LiAlCl ₄ , LiCl, LiBr, LiI, lithium chloroborane, lithium tetraphenylborate and the like can be used. Among them, ethylene carbonate or propylene carbonate and 1,2-
In a mixed solvent of dimethoxyethane and / or diethyl carbonate and / or methyl ethyl carbonate, LiC
lO ₄ , LiBF ₆ , LiPF ₆ and / or LiCF ₃ SO
An electrolytic solution in which ₃ is dissolved is preferable.

The amount of these non-aqueous electrolytes used in the battery is not particularly limited, but the required amount can be adjusted depending on the amount of active material and the size of the battery. The concentration of the lithium salt that is the supporting electrolyte is not particularly limited, but the electrolyte solution may be 1 dm ³
It is preferably 0.2 to 3.0 mol. Within this concentration range, the ionic conductivity does not decrease and the lithium salt does not precipitate.

As the separator, a microporous film or a non-woven fabric is used, and its material is, for example,
In addition to polyolefins such as polyethylene and polypropylene, fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polybutylene terephthalate, etc. (PBT) and the like.

The shape of the non-aqueous electrolyte secondary battery of the present invention may be any of coin type, button type, sheet type, laminated type, cylindrical type, flat type, square type, large type used for electric vehicles and the like. Good.

[0048]

EXAMPLES Next, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

Example 1 A composite of a material containing an element capable of forming an alloy with lithium and a conductive material was prepared as follows.

First, silicon powder having a particle diameter of 1 μm and vapor-grown carbon fiber (VGC) having a length of 5 μm and a diameter of 0.2 μm are used.
F) and graphite having a particle diameter of 2 μm, silicon: VGCF:
Graphite was mixed at a mass ratio of 60:10:30, and tumbled and granulated using a planetary ball mill. As a result, the average particle size is 15
Composite particles of μm were obtained. Then, using benzene as a carbon source, a chemical vapor deposition method (CVD) is performed to obtain a temperature of 10
The surface of the composite particles was coated with carbon at 00 ° C. The amount of carbon coated was determined from the change in mass before and after coating. The composition of the composite particles after coating was a mass ratio of silicon: VGCF: graphite: coated carbon = 56: 9: 28: 7. The average particle size of the composite particles was about 15 μm.

The negative electrode was manufactured as follows. First, 90 parts by mass of the composite particles, 5 parts by mass of carbon powder as a conductive material, and 5 parts by mass of polyvinylidene fluoride as a binder were mixed and dispersed in N-methyl-2-pyrrolidone to prepare a slurry. . The resulting slurry has a thickness of 0.
A 5 mm nickel foam sheet (porosity: 98%, average pore size: 0.2 mm) was applied and dried by heating at 100 ° C.
This sheet was punched into a circular shape having a diameter of 16 mm, pressed by a press, and its thickness was compressed to 0.2 mm to obtain a negative electrode. To completely remove the water contained in this negative electrode,
It was kept under reduced pressure of Pa at 120 ° C. for 24 hours and dried. The porosity of this negative electrode was 37%.

Next, a positive electrode was prepared as follows.
First, 100 parts by mass of LiMnO ₂ powder, 5 parts by mass of carbon black as a conductive material, 5 parts by mass of scaly graphite as a conductive material, and 0.7 parts by mass of polytetrafluoroethylene as a binder were mixed and dried. Diameter 16m
m, pressure-molded into pellets with a thickness of 0.1 mm, 250
It was heated and dried at ℃ to obtain a positive electrode.

A separator made of polypropylene non-woven fabric and polypropylene microporous film was used, and the electrolyte was 1 mol / d in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 1.
It was used as obtained by dissolving LiPF ₆ at a concentration of m ^3.

A coin type non-aqueous electrolyte secondary battery as shown in FIG. 1 was produced using the above negative electrode, positive electrode, separator and electrolytic solution. As shown in FIG. 1, by tightening the open end of the metal outer can 4 that also serves as the positive electrode terminal inward, the metal outer can 4 and the sealing plate 5 and the gasket 6 that also serve as the negative electrode terminal make the positive electrode 1 and the negative electrode 2 And the separator 3 impregnated with the electrolytic solution is sealed. The impregnation of the electrode and the like with the electrolytic solution and the sealing of the battery were performed in a glove box in a dry air atmosphere with a dew point of -50 ° C.

Using the coin type non-aqueous electrolyte secondary battery, the charge / discharge cycle characteristics were examined under the following conditions. That is, charging was performed at a constant current with a current density of 0.5 mA / cm ² .
After the charging voltage reached 120 mV, charging was performed at a constant voltage until the current density became 1/10. The discharge has a current density of 0.
Performed at a constant current of 5 mA / cm ² , the discharge end voltage is 1.5
It was set to V. As a result, the discharge capacity at the second cycle and the capacity retention rate at the 50th cycle were each 1000 mAh /
g, 95%. The discharge capacity was calculated per 1 g of the composite particles. The capacity retention rate at the 50th cycle is 50
It was calculated by dividing the discharge capacity at the second cycle by the discharge capacity at the second cycle.

Further, a model cell was prepared by combining the above negative electrode and metallic lithium and using the same electrolytic solution and separator as above. Using this model cell, the change in thickness of the negative electrode was investigated. As a result, 10
The thickness of the negative electrode when charged to 00 mAh / g is 0.25.
mm, and the coefficient of expansion of the thickness of the negative electrode was 125% when calculated from the thickness of the negative electrode before charging of 0.2 mm.

(Example 2) In place of the nickel foam sheet, a fibrous nickel sintered mat having a thickness of 0.5 mm before pressing (aperture ratio 91%, fiber diameter 20 μm) was used. In the same manner as in Example 1, a coin type non-aqueous electrolyte secondary battery and a model cell were produced, and charge / discharge cycle characteristics and changes in the thickness of the negative electrode were similarly examined.

The discharge capacity at the second cycle and the capacity retention rate at the 50th cycle of this coin type non-aqueous electrolyte secondary battery were 1000 mAh / g and 85%, respectively. The thickness change of the negative electrode using this model cell before and after charging was 10
The thickness of the negative electrode when charged to 00 mAh / g is 0.3 m
m, and the expansion coefficient of the thickness of the negative electrode was 150% when calculated from the thickness of the negative electrode before charging of 0.2 mm.

(Example 3) Instead of the nickel foam sheet, a copper foam sheet having a thickness of 0.6 mm before pressing (aperture ratio 96%, average pore diameter 0.2 mm) was used. A coin type non-aqueous electrolyte secondary battery and a model cell were produced in the same manner as in Example 1 except that a negative electrode (thickness 0.3 mm, porosity 34%) was used, and charge / discharge cycle characteristics and negative electrode The change in thickness was examined.

The discharge capacity at the second cycle and the capacity retention rate at the 50th cycle of this coin type non-aqueous electrolyte secondary battery were 1000 mAh / g and 92%, respectively. The thickness change of the negative electrode using this model cell before and after charging was 10
The thickness of the negative electrode when charged to 00 mAh / g is 0.42.
mm, and the coefficient of expansion of the thickness of the negative electrode was 140% when calculated from the thickness of the negative electrode before charging of 0.3 mm.

Comparative Example 1 A negative electrode (thickness 0.07 mm, porosity 28%) produced by using a copper foil having a thickness of 10 μm was used in place of the nickel foam sheet, except that a nickel foil was used.
A coin type non-aqueous electrolyte secondary battery and a model cell were prepared in the same manner as in Example 1, and charge / discharge cycle characteristics and changes in the thickness of the negative electrode were similarly examined.

The discharge capacity at the second cycle and the capacity retention rate at the 50th cycle of this coin type non-aqueous electrolyte secondary battery were 1000 mAh / g and 60%, respectively. The thickness change of the negative electrode using this model cell before and after charging was 10
The thickness of the negative electrode when charged to 00 mAh / g is 0.16
mm, and the expansion coefficient of the thickness of the negative electrode was 229% when calculated from the thickness of the negative electrode before charging of 0.07 mm.

Comparative Example 2 A negative electrode (thickness 0.2 mm, porosity 36%) prepared by using silicon powder having a particle diameter of 5 μm instead of the composite particles used in Example 1 was used. In the same manner as in Example 1, a coin type non-aqueous electrolyte secondary battery and a model cell were produced, and charge / discharge cycle characteristics and changes in the thickness of the negative electrode were similarly examined.

The discharge capacity at the second cycle and the capacity retention rate at the 50th cycle of this coin type non-aqueous electrolyte secondary battery were 1500 mAh / g and 10%, respectively. The thickness change of the negative electrode using this model cell before and after charging was 10
The thickness of the negative electrode is 0.33 when charged to 00 mAh / g.
mm, and the expansion coefficient of the thickness of the negative electrode was 165% when calculated from the thickness of the negative electrode before charging of 0.2 mm.

[0065]

As described above, according to the present invention, a current collector having a three-dimensional structure is provided with a composite of a conductive material and a material containing an element capable of forming an alloy with lithium. By using a negative electrode filled with a negative electrode material that contains the electrode, expansion and contraction of the electrode does not increase even after repeated charge and discharge cycles, the conductive network inside the electrode is not destroyed, and the battery capacity decreases and internal resistance decreases. It is possible to provide a non-aqueous electrolyte secondary battery having a high energy density that does not increase.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a coin type non-aqueous electrolyte secondary battery of the present invention.

[Explanation of symbols] 1 positive electrode 2 Negative electrode 3 separator 4 metal exterior cans 5 Seal plate 6 gasket

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Atsushi Ueda             Hitachi Ma, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. (72) Inventor Shigeo Aoyama             Hitachi Ma, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. F-term (reference) 5H017 AA03 CC27 CC28 EE01 EE04                       EE09                 5H029 AJ03 AJ06 AK04 AK05 AL01                       AL06 AL18 AM03 DJ07 EJ01                       EJ03                 5H050 AA07 AA08 BA16 CA10 CA11                       CB01 CB07 CB29 DA04 DA06                       DA07 EA10

Claims (8)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein as the negative electrode, an alloy with lithium is formed on a current collector having a three-dimensional structure. A non-aqueous electrolyte secondary battery using an electrode filled with a negative electrode material containing a composite of a material containing a possible element and a conductive material. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode is obtained by filling the negative electrode material together with a binder in the current collector and pressing the current collector. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode has a thickness of 0.1 to 10 mm and a porosity of 20 to 50%. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the current collector is made of a foamed metal or a fibrous metal sintered body. 5. The non-aqueous electrolyte secondary battery according to claim 4, wherein the foamed metal or the fibrous metal sintered body is made of a metal containing at least one selected from the group consisting of nickel and copper. 6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the element capable of forming an alloy with lithium is silicon. 7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the composite contains an element capable of forming an alloy with the lithium in a range of 30 to 80 mass%. 8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the particle surface of the composite is coated with carbon.