JP2002157996A - Negative electrode and battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode capable of improving anti-separation strength of a negative electrode current collector and a negative electrode mix layer, and a battery using this negative electrode. SOLUTION: Belt-like positive electrode 21 and negative electrode 22 have a winding electrode body wound via a separator 23. Lithium metal deposits on the negative electrode 22 in the middle of charging, and capacity of the negative electrode 22 is expressed by the sum of a capacitive component by storage-release of lithium and a capacitive component by deposit-dissolution of the lithium metal. Roughened surface work is applied to the negative electrode current collector 22a, and anti-separation strength of a negative electrode current collector layer 22b is improved thereby. Thus, even if the lithium metal deposits on a surface of a negative electrode material, separation of the negative electrode mix layer 22b is prevented, and a cycle characteristic is improved. Surface roughness of the negative electrode current collector 22a is desirably 0.1 μm or more, and the thickness of a flat part of the negative electrode current collector 22a is desirably 5 μm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode having a capacity represented by the sum of a capacity component caused by insertion and extraction of a light metal and a capacity component caused by deposition and dissolution of a light metal, and a battery provided with the same.

[0002]

2. Description of the Related Art In recent years, portable electronic devices typified by a camera-integrated VTR (video tape recorder), a mobile phone and a laptop computer have become widespread, and there is a strong demand for long-time continuous driving thereof. Along with this, demands for higher capacity and higher energy density of secondary batteries as those portable power sources are increasing.

[0003] As a secondary battery capable of obtaining a high energy density, for example, a lithium ion secondary battery using a material capable of inserting and extracting lithium (Li) such as a carbon material for the negative electrode, or a negative electrode There is a lithium secondary battery using lithium metal. In particular, lithium secondary batteries have a theoretical electrochemical equivalent of lithium metal of 205.
Since it is as large as 4 mAh / dm ³ , corresponding to 2.5 times that of the graphite material used in the lithium ion secondary battery, it is expected that a higher energy density than the lithium ion secondary battery can be obtained. Until now, many researchers have conducted research and development on the practical application of lithium secondary batteries (for example, Lithium Battery).
es, edited by Jean-Paul Gabano, Acad
emic Press (1983)).

[0004]

However, since the lithium secondary battery utilizes the precipitation / dissolution reaction of lithium metal in the negative electrode, the volume of the negative electrode greatly changes during charge and discharge, and the charge / discharge cycle characteristics are poor. Bad and difficult to put to practical use.

Accordingly, the present inventors have newly developed a secondary battery in which the capacity of the negative electrode is represented by the sum of a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium. In this method, a carbon material capable of inserting and extracting lithium is used for a negative electrode, and lithium is deposited on the surface of the carbon material during charging. According to this secondary battery, it is expected that the cycle characteristics are improved while achieving a high energy density. However, in this secondary battery, there is a problem that the capacity of the negative electrode is greatly deteriorated due to the charge / discharge cycle as compared with the lithium ion secondary battery, and the cycle characteristics are easily deteriorated.

It is considered that this deterioration is caused by peeling of the negative electrode material from the negative electrode current collector with charging and discharging.
For example, in a negative electrode in which a negative electrode mixture layer containing graphite as a negative electrode material is provided on a negative electrode current collector, when charged, lithium metal is deposited on an adhesion interface between graphite particles and an adhesion interface between graphite particles and the current collector. Therefore, if the bonding strength of these bonding interfaces is insufficient, interface destruction occurs due to precipitation of lithium metal, and as a result, the current collecting performance of the negative electrode is deteriorated. Further, the deterioration of the current collecting performance promotes an increase in the polarization phenomenon at the time of the charge / discharge reaction, and the chemical deterioration of the electrolyte is induced on the surfaces of the positive electrode and the negative electrode. As described above, it is considered that interfacial destruction due to precipitation of lithium metal causes deterioration of current collection performance and electrolyte, resulting in deterioration of cycle characteristics.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a negative electrode capable of improving the peel strength between a negative electrode current collector and a negative electrode mixture layer, and a battery using the same. It is in.

[0008]

The negative electrode according to the present invention has a negative electrode current collector having a pair of opposing surfaces, and a negative electrode mixture layer capable of inserting and extracting light metal, and has a capacity of: Expressed by the sum of the capacity component due to occlusion and release of light metal and the capacity component due to precipitation and dissolution of light metal,
The negative electrode current collector has a roughened surface.

A battery according to the present invention comprises a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative electrode current collector having a pair of opposing surfaces and a negative electrode collector capable of inserting and extracting light metal. The capacity of the negative electrode is represented by the sum of the capacity component due to occlusion and desorption of the light metal and the capacity component due to deposition and dissolution of the light metal, and the negative electrode current collector has a roughened surface. is there.

In the negative electrode according to the present invention, since the negative electrode current collector is roughened, the peel strength between the negative electrode current collector and the negative electrode mixture layer is improved. Therefore, even if light metal is deposited,
The negative electrode mixture layer is hardly peeled off from the negative electrode current collector.

In the battery according to the present invention, since the negative electrode of the present invention is used, even if lithium metal is deposited on the negative electrode during the charging reaction, the negative electrode mixture layer is hardly peeled off from the negative electrode current collector. Therefore, battery characteristics are improved.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a sectional structure of a secondary battery according to one embodiment of the present invention. This secondary battery is a so-called jelly-roll type battery. A band-shaped positive electrode 21 and a negative electrode 2 are provided inside a substantially hollow cylindrical battery can 11.
Electrode body 2 wound with a separator 2 via a separator 23
It has 0. The battery can 11 is made of, for example, nickel-plated iron, and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are respectively arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

At the open end of the battery can 11, a battery cover 14 is provided.
And a safety valve mechanism 15 provided inside the battery lid 14.
And thermal resistance element (Positive Temper)
atture Coefficient: PTC element) 1
6 is attached by caulking via a gasket 17, and the inside of the battery can 11 is sealed. The battery cover 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the thermal resistance element 16,
When the internal pressure of the battery becomes higher than a certain level due to an internal short circuit or external heating, the disk plate 15a is inverted and the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. The thermal resistance element 16 limits the current by increasing the resistance value when the temperature rises and prevents abnormal heat generation due to a large current, and is made of, for example, barium titanate-based semiconductor ceramics. The gasket 17 is made of, for example, an insulating material, and its surface is coated with asphalt.

The wound electrode body 20 is wound around, for example, a center pin 24. Positive electrode 2 of wound electrode body 20
1 is connected to a positive electrode lead 25 made of aluminum or the like, and the negative electrode 22 is connected to a negative electrode lead 26 made of nickel or the like. The positive electrode lead 25 is electrically connected to the battery cover 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

FIG. 2 is an enlarged view of a part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode mixture layer 21b is provided on both surfaces of a positive electrode current collector 21a having a pair of opposing surfaces. Although not shown, the positive electrode mixture layer 21b may be provided only on one side of the positive electrode current collector 21a. Positive electrode current collector 21a
Has a thickness of, for example, about 5 μm to 50 μm, and is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode mixture layer 21b has a thickness of, for example, 80 μm to 250 μm and includes a positive electrode material capable of inserting and extracting lithium as a light metal. When the positive electrode mixture layer 21b is provided on both surfaces of the positive electrode current collector 21a, the thickness of the positive electrode mixture layer 21b is the total thickness thereof.

As the positive electrode material capable of inserting and extracting lithium, for example, a lithium-containing compound such as lithium oxide, lithium sulfide or an intercalation compound containing lithium is suitable. You may use it. In particular, in order to increase the energy density, a lithium composite oxide represented by the general formula Li _x MO ₂ or an intercalation compound containing lithium is preferable. In addition, M is preferably one or more transition metals. Specifically, cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), aluminum (Al), vanadium (V) and titanium ( At least one of Ti)
Species are preferred. x differs depending on the charge / discharge state of the battery, and is usually a value in the range of 0.05 ≦ x ≦ 1.10. In addition, LiM having a spinel type crystal structure is also used.
n ₂ O ₄ or LiF having an olivine type crystal structure
ePO _{4 and the} like are also preferable because a high energy density can be obtained.

Incidentally, such a positive electrode material includes, for example, lithium carbonate, nitrate, oxide or hydroxide,
It is prepared by mixing a transition metal carbonate, nitrate, oxide or hydroxide to have a desired composition, pulverizing, and firing in an oxygen atmosphere at a temperature in the range of 600 to 1000 ° C. You.

The positive electrode mixture layer 21b also contains, for example, a conductive agent, and may further contain a binder, if necessary. Examples of the conductive agent include carbon materials such as graphite, carbon black and Ketjen black, and one or more of them are used in combination. Further, in addition to the carbon material, a metal material or a conductive polymer material may be used as long as the material has conductivity. Examples of the binder include synthetic rubbers such as styrene-butadiene rubber, fluorine rubber and ethylene propylene diene rubber, and polymer materials such as polyvinylidene fluoride, and one or more of them are mixed. Used as For example,
When the positive electrode 21 and the negative electrode 22 are wound as shown in FIG. 1, it is preferable to use a highly flexible styrene-butadiene-based rubber or a fluorine-based rubber as the binder.

The negative electrode 22 has, for example, a structure in which a negative electrode mixture layer 22b is provided on both surfaces of a negative electrode current collector 22a having a pair of opposing surfaces. Although not shown, the negative electrode mixture layer 22b may be provided only on one side of the negative electrode current collector 22a. The negative electrode current collector 22a is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil having good electrochemical stability, electric conductivity, and mechanical strength. In particular, copper foil is most preferable because it has high electric conductivity. The thickness of the negative electrode current collector 22a is preferably, for example, about 6 μm to 40 μm. 6μ
If the thickness is smaller than m, the mechanical strength is reduced, the anode current collector 22a is easily broken in the manufacturing process, and the production efficiency is reduced. The volume ratio becomes larger than necessary,
This is because it becomes difficult to increase the energy density.

The surface of at least a part of the negative electrode current collector 22a is roughened. FIG. 3 shows the negative electrode current collector 22.
6 is a laser microscope photograph showing the surface state of a. As described above, the surface of the negative electrode current collector 22a is formed with unevenness due to roughening, and the peel strength of the negative electrode mixture layer 22b can be improved by the anchor effect due to the unevenness. Such roughening is performed by, for example, a chemical method such as electrolytic plating or chemical plating, or a physical polishing such as sandblasting. In particular, it is preferable to use a chemical method such as an electrolytic plating process or a chemical plating process, because the projections can be formed on the copper foil with different kinds of metals. In addition, the thing where the projection part was formed by the dissimilar metal on the copper foil,
Included in roughened copper foil.

At least one surface of the negative electrode current collector 22a,
That is, the surface roughness of at least the surface provided with the negative electrode mixture layer 22b is preferably 0.1 μm or more as a 10-point average roughness according to JIS standard B0601. If it is smaller than this, the effect of improving the peel strength by the roughening cannot be sufficiently obtained. The surface roughness of a pair of surfaces of the negative electrode current collector 22a is JIS B0601.
Is preferably not more than the value defined by the following equation (2).

[0023]

## EQU2 ## {Thickness of negative electrode current collector (μm) −5 (μm)} / N (N is 1 when only one of a pair of surfaces is roughened, and both surfaces are roughened. (If processed, it is 2.)

The peel strength can be increased as the surface roughness increases. However, if the surface roughness is too large, the thickness of the flat portion of the negative electrode current collector 22a becomes thin, and the electric resistance increases. The thickness of the flat portion of the negative electrode current collector 22a is preferably 5 μm or more.
“μm” means the minimum thickness of the flat part. In the present specification, the thickness of the flat portion refers to the thickness of the negative electrode current collector 22.
It means the thickness obtained by subtracting the surface roughness of both surfaces from the thickness of a. The ten-point average roughness is, as shown in Expression 3, a portion extracted from the roughness curve in the direction of the average line by a reference length, and a portion from the highest peak to the fifth peak of the extracted portion is obtained. It means the sum of the average of the absolute values of the altitudes (Yp _{1 to} Yp ₅ ) and the average of the absolute values of the altitudes (Yv _{1 to} Yv ₅ ) from the lowest valley to the fifth valley. In this specification, the reference length is 0.08
mm, and the evaluation length was 0.4 mm.

[0025]

(Equation 3)

The negative electrode mixture layer 22b includes a negative electrode material capable of inserting and extracting lithium as a light metal.
It may contain the same binder as b. In this specification, the term "storage / release of light metal" means that light metal ions are electrochemically stored / released without losing their ionicity. The thickness of the negative electrode mixture layer 22b is, for example, 80 μm to 250 μm. This thickness is the total thickness when the negative electrode mixture layer 22b is provided on both surfaces of the negative electrode current collector 22a.

As the negative electrode material capable of inserting and extracting lithium, for example, a carbon material, a metal compound,
Crystalline or amorphous silicon, silicon compounds,
LiN ₃ or a polymer material is used, and one or more of them are used in combination. Examples of the carbon material include graphite, non-graphitizable carbon, and easily graphitizable carbon, and the metal compound is SnSi.
Oxides such as O ₃ or SnO ₂ are mentioned, and silicon compounds include silicon oxides and nitrides, and polymer materials include polyacetylene, polyaniline and polypyrrole.

Among them, a carbon material is preferable because a change in crystal structure that occurs during charge and discharge is very small, a high charge and discharge capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite has a large electrochemical equivalent,
It is preferable because a high energy density can be obtained.

As the graphite, for example, the true density is 2.10
g / cm ³ or more, preferably 2.18 g / cm ³
The above is more preferable. In order to obtain such a true density, the C-axis crystallite thickness of the (002) plane must be 1
It is necessary to be 4.0 nm or more. Also, (00
2) The spacing between the surfaces is preferably less than 0.340 nm, and more preferably 0.335 nm or more and 0.337 nm or less.

The graphite may be natural graphite or artificial graphite.
In the case of artificial graphite, for example, it can be obtained by carbonizing an organic material, performing a high-temperature heat treatment, and pulverizing and classifying. The high-temperature heat treatment is performed by, for example, carbonizing at 300 ° C. to 700 ° C. in an inert gas stream such as nitrogen (N ₂ ) as necessary,
The temperature is raised from 900 ° C to 1500 ° C at a rate of 1 ° C to 100 ° C per minute, the temperature is maintained for about 0 hours to 30 hours, and calcined, and heated to 2000 ° C or more, preferably 2500 ° C or more. This is performed by maintaining the temperature for an appropriate time.

As the organic material used as a starting material, coal or pitch can be used. For the pitch, for example, tars obtained by pyrolyzing coal tar, ethylene bottom oil or crude oil at a high temperature, asphalt, etc. (vacuum distillation, normal pressure distillation or steam distillation), thermal polycondensation, extraction, Examples include those obtained by chemical polycondensation, those produced at the time of wood reflux, polyvinyl chloride resin, polyvinyl acetate, polyvinyl butyrate, and 3,5-dimethylphenol resin.
These coals or pitches have a maximum of 400
It exists as a liquid at about ℃, and aromatic rings are condensed and polycyclic by being held at that temperature, and it is in a laminated orientation state, and then becomes a solid carbon precursor at about 500 ° C. or higher, that is, semi-coke. (Liquid phase carbonization process).

Examples of the organic material include condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphen, and pentacene, and derivatives thereof (for example, carboxylic acids and carboxylic anhydrides of the above compounds). , Carboximides), or mixtures thereof. Further, condensed heterocyclic compounds such as acenaphthylene, indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthridine and derivatives thereof;
Alternatively, a mixture thereof can be used.

The pulverization may be carried out before or after carbonization or calcination, or during the heating process before graphitization. In these cases, heat treatment for graphitization is finally performed in a powder state. However, to obtain graphite powder with high bulk density and high breaking strength, heat treatment is performed after molding the raw material,
It is preferable to pulverize and classify the obtained graphitized molded body.

For example, when producing a graphitized molded body, coke as a filler and binder pitch as a molding agent or a sintering agent are mixed and molded. And the pitch impregnating step of impregnating the sintered body with the melted binder pitch is repeated several times, followed by heat treatment at a high temperature. The impregnated binder pitch is carbonized and graphitized in the above heat treatment process. By the way, in this case,
Since filler (coke) and binder pitch are used as raw materials, it is graphitized as a polycrystal, and since sulfur and nitrogen contained in the raw materials are generated as a gas during heat treatment, minute holes are formed in the passage. It is formed. Accordingly, the vacancies facilitate the progress of the insertion and extraction reaction of lithium, and also have the advantage of high industrial processing efficiency. In addition, as a raw material of the molded body, the moldability itself,
A filler having sinterability may be used. In this case, it is not necessary to use a binder pitch.

As the non-graphitizable carbon, the (002) plane spacing is 0.37 nm or more and the true density is 1.70 g / cm.
³ and differential thermal analysis in air (diff)
erential thermal analysis
s; DTA) does not show an exothermic peak at 700 ° C. or higher.

Such non-graphitizable carbon can be obtained, for example, by subjecting an organic material to a heat treatment at about 1200 ° C., followed by pulverization and classification. The heat treatment is, for example, 3
After carbonization at 00 ° C to 700 ° C (solid carbonization process),
The temperature is raised from 900 ° C. to 1300 ° C. at a rate of 1 ° C. to 100 ° C. per minute, and the temperature is maintained for about 0 to 30 hours. The pulverization may be performed before or after carbonization, or during the heating process.

As the organic material as a starting material, for example, furfuryl alcohol or furfural polymer or copolymer, or furan resin which is a copolymer of these polymers with other resins can be used. . Also,
Phenol resin, acrylic resin, vinyl halide resin, polyimide resin, polyamide imide resin, polyamide resin, conjugated resin such as polyacetylene or polyparaphenylene, cellulose or derivatives thereof, coffee beans, bamboo, shellfish including chitosan, bacteria Biocelluloses utilizing the same can also be used. Furthermore, the atomic ratio H / of hydrogen atoms (H) and carbon atoms (C)
A compound in which a functional group containing oxygen (O) is introduced (so-called oxygen cross-linking) into petroleum pitch in which C is, for example, 0.6 to 0.8 can also be used.

The oxygen content of this compound is preferably at least 3%, more preferably at least 5% (see JP-A-3-25253). The oxygen content affects the crystal structure of the carbon material, and at a higher content, the physical properties of the non-graphitizable carbon can be increased.
This is because the capacity of the negative electrode can be improved. Incidentally, petroleum pitch is used for distillation (vacuum distillation, atmospheric distillation or steam distillation) of tars obtained by pyrolyzing coal tar, ethylene bottom oil or crude oil at a high temperature, or hot distillation. It is obtained by condensation, extraction or chemical polycondensation.
Examples of the oxidative cross-linking method include a wet method in which an aqueous solution of nitric acid, sulfuric acid, hypochlorous acid, or a mixed acid thereof is reacted with petroleum pitch, and an oxidizing gas such as air or oxygen is reacted with petroleum pitch. Or a method of reacting a solid reagent such as sulfur, ammonium nitrate, ammonium persulfate, or ferric chloride with petroleum pitch.

The organic material used as the starting material is not limited to these, and any other organic material may be used as long as it is an organic material that can be made non-graphitizable carbon through a solid phase carbonization process by oxygen crosslinking or the like.

Examples of the non-graphitizable carbon include those produced using the above-mentioned organic materials as starting materials, and those described in JP-A-3-3-1.
A compound containing phosphorus (P), oxygen and carbon as main components described in 37010 is also preferable because it shows the above-mentioned physical property parameters.

Further, in this secondary battery, during the charging process, lithium metal starts to precipitate on the negative electrode 22 when the open circuit voltage (that is, the battery voltage) is lower than the overcharge voltage. That is, the capacity of the negative electrode 22 is represented by the sum of a capacity component due to insertion and extraction of lithium and a capacity component due to deposition and dissolution of lithium metal. The overcharge voltage refers to an open circuit voltage when the battery is in an overcharged state. For example, one of the guidelines set by the Japan Storage Battery Association (Battery Manufacturers Association) is “lithium secondary battery”. Refers to voltages higher than the open circuit voltage of a "fully charged" battery as defined and defined in the "Safety Evaluation Guidelines" (SBA G1101).

Thus, in this secondary battery, a high energy density can be obtained and the cycle characteristics can be improved. This is similar to a conventional lithium secondary battery in that lithium metal is deposited on the negative electrode 15, but by depositing lithium metal on a negative electrode material capable of inserting and extracting lithium, the This is because it is considered that the volume change of the negative electrode 22 due to charge and discharge can be reduced while maintaining the capacity. That is, in the present embodiment, both the negative electrode material capable of inserting and extracting lithium and the lithium metal function as the negative electrode active material.

The separator 23 is made of, for example, a porous film made of a synthetic resin such as polytetrafluoroethylene, polypropylene or polyethylene, or a porous film made of ceramic. The structure may be modified. Above all, a polyolefin porous film is preferable because it has an excellent short-circuit prevention effect and can improve battery safety by a shutdown effect. In particular, polyethylene is 100
Since a shutdown effect can be obtained in the range of not less than 160 ° C. and the electrochemical stability is excellent, it is preferable as a material forming the separator 16. In addition, polypropylene is also preferable, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

The porous film made of polyolefin is prepared, for example, by kneading a liquid polyolefin composition in a molten state with a low-volatility solvent in a liquid state in a molten state to obtain a uniform high-concentration solution of the polyolefin composition. Molded by
It is obtained by cooling into a gel-like sheet and stretching.

As the low volatile solvent, for example, nonane,
Low volatile aliphatic or cyclic hydrocarbons such as decane, decalin, p-xylene, undecane or liquid paraffin can be used. The mixing ratio of the polyolefin composition and the low-volatile solvent is 100% by mass of the total of both.
The content of the polyolefin composition is preferably from 10% by mass to 80% by mass, and more preferably from 15% by mass to 70% by mass. If the amount of the polyolefin composition is too small, swelling or neck-in becomes large at the die exit during molding, and sheet molding becomes difficult. on the other hand,
If the amount of the polyolefin composition is too large, it is difficult to prepare a uniform solution.

When a high-concentration solution of the polyolefin composition is molded with a die, in the case of a sheet die, the gap is preferably, for example, 0.1 mm or more and 5 mm or less. Further, the extrusion temperature is preferably from 140 ° C. to 250 ° C., and the extrusion speed is preferably from 2 cm / min to 30 cm / min.

The cooling is performed to at least the gelling temperature or lower. As a cooling method, a method of directly contacting with cold air, cooling water, or another cooling medium, a method of contacting with a roll cooled by a refrigerant, or the like can be used. The high-concentration solution of the polyolefin composition extruded from the die may be taken at a take-up ratio of 1 to 10 and preferably 1 to 5 before or during cooling. If the take-up ratio is too large, neck-in becomes large, and breakage tends to occur during stretching, which is not preferable.

The stretching of the gel-like sheet is preferably carried out by biaxial stretching, for example, by heating this gel-like sheet and employing a tenter method, a roll method, a rolling method or a combination thereof. At that time, either vertical or horizontal simultaneous stretching or sequential stretching may be used, but simultaneous secondary stretching is particularly preferable.
The stretching temperature is preferably equal to or lower than the temperature obtained by adding 10 ° C. to the melting point of the polyolefin composition, and more preferably equal to or higher than the crystal dispersion temperature and lower than the melting point. If the stretching temperature is too high, an effective molecular chain orientation due to stretching cannot be performed due to melting of the resin, which is not preferable.If the stretching temperature is too low, the softening of the resin becomes insufficient and the film breaks during stretching. This is because it is easy to perform stretching at a high magnification.

After stretching the gel-like sheet, it is preferable to wash the stretched film with a volatile solvent to remove the remaining low-volatile solvent. After washing, the stretched film is dried by heating or blowing, and the washing solvent is volatilized. As the cleaning solvent, for example, pentane, hexane,
A volatile substance such as a hydrocarbon such as hebutane, a chlorinated hydrocarbon such as methylene chloride or carbon tetrachloride, a fluorocarbon such as ethane trifluoride, or an ether such as diethyl ether or dioxane is used. The washing solvent is selected according to the low-volatile solvent used, and used alone or in combination. The washing can be performed by a method of immersing in a volatile solvent for extraction, a method of sprinkling with a volatile solvent, or a method of combining these. This washing is performed until the residual low-volatile solvent in the stretched film becomes less than 1 part by mass with respect to 100 parts by mass of the polyolefin composition.

The separator 23 is impregnated with an electrolytic solution which is a liquid electrolyte. This electrolytic solution is obtained by dissolving a lithium salt as an electrolyte salt in a liquid non-aqueous solvent. The liquid non-aqueous solvent is, for example, a non-aqueous compound having an intrinsic viscosity at 25 ° C. of 10.0 mPa · s or less. As such a non-aqueous solvent, for example, a solvent having relatively high electrochemical stability such as ethylene carbonate, propylene carbonate, diethyl carbonate or methyl ethyl carbonate is preferably used as a main solvent. Any one of these may be used as the main solvent, or a mixture of two or more thereof may be used.

As the non-aqueous solvent, the following auxiliary solvents may be mixed with the main solvent. As the secondary solvent, for example, butylene carbonate, γ-butyrolactone, γ-
Valerolactone, those obtained by substituting a part or all of the hydrogen groups of these compounds with fluorine groups, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan , Methyl acetate, methyl propionate, dimethyl carbonate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropyronitrile, N, N-dimethylformamide,
N-methylpyrrolidinone, N-methyloxazolidinone, N, N-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethylsulfoxide, or trimethyl phosphate, any one or more of these May be used in combination.

As the lithium salt, for example, LiP
F ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , Li
B (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO
₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ C
F ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCL or LiBr are suitable, and one or more of these are used in combination. Above all, LiPF ₆ is preferable because high ion conductivity can be obtained and cycle characteristics can be further improved. The concentration of the lithium salt with respect to the non-aqueous solvent is preferably 2.0 mol / kg or less.
More preferably, it is 5 mol / kg or more. This is because the ionic conductivity of the electrolytic solution can be increased within this range.

In place of the electrolytic solution, a gel electrolyte in which the host polymer compound holds the electrolytic solution may be used. The gel electrolyte has an ionic conductivity of 1 mS /
cm or more, and there is no particular limitation on the composition and the structure of the host polymer compound. The electrolyte (that is, the liquid non-aqueous solvent and the electrolyte salt) is as described above. As the host polymer compound, for example, polyacrylonitrile, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and polyhexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, poly Examples include siloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene and polycarbonate. In particular, from the viewpoint of electrochemical stability, it is desirable to use a polymer compound having a structure of polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide. The amount of the host polymer compound added to the electrolyte depends on the compatibility of the two, but it is usually preferable to add a host polymer compound corresponding to 5 to 50% by mass of the electrolyte.

The concentration of the lithium salt is preferably 2.0 mol / kg or less, more preferably 0.5 mol / kg or more with respect to the non-aqueous solvent, similarly to the electrolytic solution. However, the term "non-aqueous solvent" is not limited to a liquid non-aqueous solvent, but is a concept that broadly includes one that dissociates an electrolyte salt. Thus, when a host polymer having ion conductivity is used, the host polymer is also included in the non-aqueous solvent.

This secondary battery can be manufactured, for example, as follows.

First, for example, a positive electrode material is prepared by mixing a positive electrode material capable of inserting and extracting lithium, a conductive agent, and a binder, and this positive electrode mixture is mixed with N-methyl-2. −
It is dispersed in a solvent such as pyrrolidone to form a paste-like positive electrode mixture slurry. This positive electrode mixture slurry is mixed with the positive electrode current collector 2
After coating on 1a and drying the solvent, the positive electrode mixture layer 21b is formed by compression molding using a roller press or the like, and the positive electrode 21 is manufactured.

Next, for example, a negative electrode mixture is prepared by mixing a negative electrode material capable of inserting and extracting lithium and a binder, and the negative electrode mixture is mixed with N-methyl-2-pyrrolidone or the like. Dispersed in a solvent to form a paste-like negative electrode mixture slurry. The negative electrode mixture slurry is applied to the negative electrode current collector 22a, the solvent is dried, and then compression-molded by a roller press or the like to form the negative electrode mixture layer 22b, thereby producing the negative electrode 22.

Subsequently, the cathode lead 25 is attached to the cathode current collector by welding or the like, and the anode lead 26 is attached to the anode current collector by welding or the like. After that, the positive electrode 2
1 and the negative electrode 22 are wound via the separator 23, and the distal end of the positive electrode lead 26 is welded to the safety valve mechanism 15, and the distal end of the negative electrode lead 27 is welded to the battery can 11.
The wound positive electrode 21 and negative electrode 22 are connected to a pair of insulating plates 12,
13 and housed inside the battery can 11. After housing the positive electrode 21 and the negative electrode 22 inside the battery can 11, an electrolyte is injected into the inside of the battery can 11 and impregnated into the separator 23. After that, the battery lid 14,
The safety valve mechanism 15 and the thermal resistance element 16 are
Fix by swaging through 7. This allows
The secondary battery shown in FIG. 1 is formed.

This secondary battery operates as follows.

In this secondary battery, when charged, lithium ions are released from the positive electrode mixture layer 21b, and the separator 2
First, the negative electrode mixture layer 22 is laid through the electrolyte impregnated in the negative electrode mixture layer 22.
The lithium contained in b is stored in a negative electrode material that can be inserted and extracted. When charging is further continued, in the state where the open circuit voltage is lower than the overcharge voltage, the charge capacity exceeds the charge capacity capacity of the negative electrode material capable of inserting and extracting lithium, and the charge capacity is increased on the surface of the anode material capable of inserting and extracting lithium. Lithium metal begins to precipitate. Thereafter, lithium metal continues to be deposited on the negative electrode 22 until charging is completed.

Next, when discharging is performed, first, lithium metal deposited on the negative electrode 22 is eluted as an ion, and the positive electrode mixture layer 21 is passed through the electrolytic solution impregnated in the separator 23.
b. When the discharge is further continued, the negative electrode mixture layer 22
The lithium ions occluded in the negative electrode material capable of occluding and releasing lithium in b are released and occluded in the positive electrode mixture layer 21b via the electrolytic solution. Therefore, in this secondary battery, characteristics of both the conventional so-called lithium secondary battery and lithium ion secondary battery, that is, high energy density and good cycle characteristics can be obtained.

In particular, in the present embodiment, the negative electrode current collector 22a
Since the surface is roughened, the peel strength between the negative electrode current collector 22a and the negative electrode mixture layer 22b is improved, and even if lithium metal is deposited on the surface of the negative electrode material during charging, the negative electrode current collector The negative electrode mixture layer 22b is hardly peeled off from the base material 22a. Therefore, even if charging and discharging are repeated, deterioration of the current collecting performance and deterioration of the electrolyte are prevented, and the cycle characteristics are improved.

As described above, according to the present embodiment, since the negative electrode current collector 22a is roughened, the peel strength between the negative electrode current collector 22a and the negative electrode mixture layer 22b can be improved. Even if lithium metal is deposited on the surface of the negative electrode material during charging, the negative electrode mixture layer 22b can be prevented from peeling off. Therefore, even if charge and discharge are repeated, a decrease in capacity can be prevented, and cycle characteristics can be improved.

In particular, the surface roughness of at least one surface of the negative electrode current collector 22a is set to 0.1 μm or more,
When the surface roughness of the pair of surfaces a is equal to or less than the value defined by the above [Equation 2] or the thickness of the flat portion is equal to or more than 5 μm, the peel strength can be sufficiently improved while keeping the electric resistance low. Can be.

[0065]

EXAMPLES Further, specific examples of the present invention will be described in detail.

(Examples 1 to 7) As Examples 1 to 7, the negative electrode material capable of inserting and extracting lithium has an average particle diameter of 25 μm.
A negative electrode using the granular graphite was prepared. First, 85% by mass of granular graphite powder, 5% by mass of fibrous graphite, and 10% by mass of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, and this was mixed with 1-methyl- as a solvent. Dispersed in 2-pyrrolidone to obtain a negative electrode mixture slurry. Next, a strip-shaped copper foil electrolytically plated was prepared as a negative electrode current collector. The thicknesses of the plating material and the negative electrode current collector are shown in Tables 1 in Examples 1 to 7.
Was changed as shown in FIG. Subsequently, the negative electrode mixture slurry was uniformly applied to one surface of the negative electrode current collector, dried, and then heated and pressed to obtain a strip-shaped negative electrode having a total thickness of 60 μm.

[0067]

[Table 1]

After that, the surface roughness (10-point average roughness) of the negative electrode current collector was measured for the negative electrodes of Examples 1 to 7 produced. Table 1 shows the results. Further, the fabricated negative electrodes of Examples 1 to 7 were cut into a circle having a diameter of 15 mm, and the coin-type cells shown in FIG. This coin-type cell is formed by laminating a disk-shaped positive electrode 32 housed in an outer can 31 and a disk-shaped negative electrode 34 housed in an outer cup 33 with a separator 35 interposed therebetween.

The outer can 31 also serves as a positive electrode terminal, and was formed by drawing a stainless steel plate. The positive electrode 32 was formed of a lithium metal plate having a charge / discharge capacity that was more than that of the negative electrode 34. Exterior cup 3
Reference numeral 3 also serves as a negative electrode terminal, and is formed by drawing a stainless steel plate in the same manner as the outer can 31 by drawing.
No. 4 was welded to this exterior cup 33. The separator 35 was formed of a polyethylene porous film having a thickness of 25 μm and pores of 35%, and was sufficiently impregnated with the electrolyte 36. Electrolyte 3
In No. ₆ , a solvent in which ethylene carbonate, propylene carbonate, and diethyl carbonate were mixed at a volume ratio of 2: 1: 5 was mixed with LiPF ₆ as a lithium salt in an amount of 1.5 m.
The solution dissolved at a concentration of ol / kg was used. Outer can 3
1 and the outer cup 33 were sealed by caulking via a gasket 37 made of polypropylene resin.
The outer dimensions of the coin cell are 20 mm in diameter and 2.5 mm in height
And

With respect to the manufactured coin-type cells of Examples 1 to 7, charging and discharging were repeated to determine the charging and discharging efficiency. that time,
The charging is performed at a constant current of 1 mA and the charging capacity of the negative electrode is 850 mA.
h / dm ³ was reached. On the other hand, the discharge was 1 mA
At a constant current of 1.5 V until the terminal voltage reached 1.5 V (vs. Li). The charge / discharge efficiency is the ratio of the discharge capacity to the charge capacity, that is, (discharge capacity / charge capacity) ×
100. Table 1 shows the charge / discharge efficiencies at the first, fifth and 30th cycles, respectively. Also,
FIG. 5 shows charge / discharge curves at the second cycle, the fifth cycle, the tenth cycle, the twentieth cycle, and the thirty cycle of Example 1.

As Comparative Examples 1 and 2 with respect to the present example, the same as the present example except that a rolled copper foil having a thickness of 12 μm and not subjected to electrolytic plating as shown in Table 1 was used as the negative electrode current collector. To produce a negative electrode. Further, coin-type cells were produced in the same manner as in this example using the produced negative electrodes of Comparative Examples 1 and 2, and the charge / discharge efficiency was determined. At that time, Comparative Example 1
Is charged and discharged under the same conditions as in this example, and Comparative Example 2 is performed until the charge capacity of the negative electrode reaches 450 mAh / dm ³ so that lithium metal does not deposit on the negative electrode during charging. Except for this, charging and discharging were performed under the same conditions as in this example. Table 1 shows the charge / discharge efficiencies at the first, fifth and 30th cycles, respectively. FIG. 6 shows the charge / discharge curves at the second cycle, the fifth cycle, the tenth cycle, the twentieth cycle and the thirty cycle of Comparative Example 1, and FIG.
2nd cycle, 5th cycle, 10th cycle, 20
The charge and discharge curves at the cycle and the 30th cycle are shown.

As can be seen from FIGS. 5 and 7, in the present embodiment, in the region A of the discharge curve corresponding to the dissolution reaction of the lithium metal on the granular graphite, the discharge corresponding to the detachment reaction of lithium ions from the granular graphite. The region B of the curve was observed. That is, according to the present embodiment, it was confirmed that the capacity of the negative electrode was represented by the sum of the capacity component due to insertion and extraction of lithium and the capacity component due to precipitation and dissolution of lithium. In this example, a larger charge / discharge capacity was obtained than in Comparative Example 2 in which lithium metal was not deposited.

Further, as can be seen from Table 1, FIGS. 5 and 6, in Examples 1 to 7, the charge / discharge efficiency at the 30th cycle was higher than in Comparative Example 1 in which the negative electrode current collector was not roughened. . That is, it was found that if the negative electrode current collector was roughened, the cycle characteristics could be improved even when lithium metal was deposited on the negative electrode. Incidentally, in Comparative Example 2 in which lithium metal was not deposited, it was confirmed that good cycle characteristics could be obtained without roughening.

Further, as can be seen by comparing Examples 1 and 2 and Examples 4 and 5, the negative electrode current collector has a surface roughness smaller than 0.1 μm. In Example 5, a sufficient effect due to the roughening was not obtained, and the cycle characteristics could not be sufficiently improved. Further, Example 1
As can be seen from a comparison between Example 3 and Example 4 and Example 4 and Example 6, Example 3 has a large surface roughness of the negative electrode current collector.
In addition, in Example 5, the polarization phenomenon at the time of the electrode reaction increased due to the decrease in the current collecting performance, and the cycle characteristics could not be sufficiently improved. Incidentally, in this embodiment, since the negative electrode current collector is roughened by electrolytic plating, both surfaces of the negative electrode current collector are roughened, and the flat surfaces of the negative electrode current collectors in Examples 3 and 5 are flattened. The thickness of the portion is 4 μm. That is, it was found that when the surface roughness of the negative electrode current collector was 0.1 μm or more and the value was not more than the value defined by the above Expression 2, or the thickness of the flat portion was 5 μm or more, the cycle characteristics could be further improved. .

In addition, as can be seen from Example 7, even when nickel plating was performed on the copper foil, the cycle characteristics could be improved. That is, it was found that the cycle characteristics could be improved even when the protrusions made of different metals were formed on the copper foil.

(Examples 8 to 14) Examples 1 to 7 and Comparative Examples 1 and 2 correspond to Examples 8 to 14 and Comparative Examples 3 and 4.
A jelly-roll secondary battery similar to that shown in FIG. 1 was prepared using the same negative electrode as described above, and its characteristics were evaluated. Here, FIG.
, And will be described using the same reference numerals as in FIG.

First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) were mixed with Li ₂ CO ₃ : CoC
O ₃ was mixed at a ratio of 0.5: 1 (molar ratio) and calcined in air at 900 ° C. for 5 hours to obtain a lithium-cobalt composite oxide (LiCoO ₂ ). An X-ray diffraction measurement of the obtained lithium-cobalt composite oxide showed a good agreement with the peak of LiCoO ₂ registered in the JCPDS file. Next, this lithium-cobalt composite oxide was pulverized to obtain a powder having a cumulative 50% particle size of 15 μm obtained by a laser diffraction method, and used as a positive electrode material. Subsequently, the lithium-cobalt composite oxide powder 9
5% by mass and 5% by mass of lithium carbonate powder were mixed, and 94% by mass of this mixture, 3% by mass of amorphous carbon powder as a conductive agent, and 3% by mass of polyvinylidene fluoride as a binder were mixed. To prepare a positive electrode mixture. After preparing the positive electrode mixture, this positive electrode mixture is dispersed in N-methylpyrrolidone as a solvent to form a positive electrode mixture slurry, which is uniformly applied to both surfaces of a positive electrode current collector 21a made of a 20-μm-thick strip-shaped aluminum foil. , Dried and compression molded to form the positive electrode mixture layer 21
Then, the positive electrode 21 having a thickness of 185 μm was formed. After that, a positive electrode lead 25 made of aluminum was attached to one end of the positive electrode current collector 21a.

The same negative electrode mixture slurry and the same negative electrode current collector 22a as in Examples 1 to 7 or Comparative Examples 1 and 2 were used.
8 to 14 and Comparative Examples 3 and 4
The negative electrode 22 was produced. The thickness and plating material of the negative electrode current collector 22a are as shown in Table 2. The negative electrode mixture layer 22b is formed on both surfaces of the negative electrode current collector 22a,
Is 90 μm for Examples 1 to 7 and Comparative Example 1 by adjusting the thickness of the negative electrode mixture layer 22 b.
For Comparative Example 2, the thickness was set to 210 μm. That is, in Comparative Example 2, the amount of the negative electrode material capable of inserting and extracting lithium was increased so that lithium metal was not deposited on the negative electrode 22 during charging. Next, the negative electrode current collector 2
A negative electrode lead 26 made of nickel was attached to one end of 2a.

After each of the positive electrode 21 and the negative electrode 22 was prepared, a separator 23 made of a stretched microporous polyethylene film having a thickness of 30 μm was prepared, and the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 were laminated in this order. Was spirally wound many times to produce a wound electrode body 20 having an outer diameter of 14 mm.

After the wound electrode body 20 has been manufactured, the wound electrode body 20 is sandwiched between a pair of insulating plates 12 and 13, and the negative electrode lead 2 is formed.
6 was welded to the battery can 11, the positive electrode lead 25 was welded to the safety valve mechanism 15, and the spirally wound electrode body 20 was housed inside the nickel-plated iron battery can 11. After that, the electrolytic solution was injected into the battery can 11 by a reduced pressure method. The electrolyte contains 20% by mass of ethylene carbonate,
LiPF was used as an electrolyte salt in a non-aqueous solvent obtained by mixing 50% by mass of dimethyl carbonate, 20% by mass of ethyl methyl carbonate, and 10% by mass of propylene carbonate.
₆ was dissolved at a concentration of 1.5 mol / kg. The injection amount of the electrolyte was 3.5 g.

After injecting the electrolyte into the battery can 11, the battery lid 14 was caulked to the battery can 11 via a gasket 17 coated with asphalt on the surface, thereby obtaining Examples 8 to 14 and Comparative Examples 3 and 4. 14m for 14m
Thus, a jelly roll type secondary battery having a height of 65 mm and a height of 65 mm was obtained.

The obtained Examples 8 to 14 and Comparative Example 3,
A charge / discharge test was performed on the secondary battery of No. 4, and the energy density and the discharge capacity ratio of the battery were determined. At that time, charging was performed at a constant current of 300 mA until the battery voltage reached 4.2 V, and then at a constant voltage of 4.2 V until the total charging time reached 5 hours. The voltage between the positive electrode 21 and the negative electrode 22 immediately before the end of charging was 4.2 V, and the current value was 5 mA or less. On the other hand, discharging was performed at a constant current of 300 mA until the battery voltage reached 2.75 V. By the way, when charging and discharging are performed under the conditions shown here, a fully charged state and a completely discharged state are obtained. The discharge capacity of the battery was defined as the discharge capacity at the second cycle, and the energy density of the battery was determined from this value. The discharge capacity ratio was calculated as the ratio of the discharge capacity at the 200th cycle to the discharge capacity at the second cycle, that is, (discharge capacity at the 300th cycle / discharge capacity at the second cycle) × 100. Table 2 shows the obtained results.

[0083]

[Table 2]

As can be seen from Table 2, according to Examples 8 to 14, a higher energy density was obtained than in Comparative Example 4 in which lithium metal was not deposited on the negative electrode 22, and the negative electrode current collector 22
A larger discharge capacity ratio was obtained than in Comparative Example 1 in which a was not roughened. That is, it was found that if the negative electrode current collector was roughened, high energy density could be obtained and cycle characteristics could be further improved. Incidentally, in Comparative Example 2 in which lithium metal was not deposited, good cycle characteristics were obtained without rough surface processing. That is, the effect of roughening the negative electrode current collector 22a is particularly effective in a negative electrode in which the capacity of the negative electrode is represented by the sum of a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium. It turned out to be effective.

Further, the discharge capacity ratios of the ninth and tenth embodiments were smaller than that of the eighth embodiment, and the twelfth and twelfth embodiments were smaller than the eleventh embodiment.
13, the discharge capacity ratio was small, and it was also found that the cycle characteristics could not be sufficiently improved unless the surface roughness of the negative electrode current collector 22a was within a predetermined range. Furthermore, a sufficient capacity ratio was obtained also in Example 14, and it was found that the cycle characteristics could be sufficiently improved even if the roughening was performed with a different kind of metal.

Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above-described embodiments and examples, and can be variously modified. For example, in the above embodiments and examples, the case where lithium is used as the light metal has been described. However, another alkali metal such as sodium (Na) or potassium (K), or magnesium (Mg) or calcium (Ca) is used. The present invention can also be applied to the case where an alkaline earth metal, other light metal such as aluminum (Al), lithium or an alloy thereof is used, and the same effect can be obtained. At this time, a negative electrode material, a positive electrode material, a non-aqueous solvent, an electrolyte salt, or the like capable of inserting and extracting a light metal is selected according to the light metal. However, it is preferable to use lithium or an alloy containing lithium as the light metal because voltage compatibility with lithium ion secondary batteries currently in practical use is high. When an alloy containing lithium is used as the light metal, a substance capable of forming an alloy with lithium exists in the electrolyte, and an alloy may be formed at the time of deposition. There is a possible substance,
An alloy may be formed during precipitation.

Further, in the above embodiments and examples, the case where a gel electrolyte which is one kind of the electrolytic solution or the solid electrolyte is used has been described, but another electrolyte may be used. Other electrolytes include, for example, an organic solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, an ion conductive ceramic,
Inorganic solid electrolytes made of ion-conductive glass or ionic crystals, or mixtures of these inorganic solid electrolytes and electrolytes, or mixtures of these inorganic solid electrolytes and gel electrolytes or organic solid electrolytes Is mentioned.

Further, in the above embodiments and examples, a cylindrical secondary battery having a wound structure has been described. However, the present invention relates to an elliptical or polygonal secondary battery having a wound structure. Alternatively, the present invention can be similarly applied to a secondary battery having a structure in which a positive electrode and a negative electrode are folded or stacked. In addition, the present invention can be applied to a secondary battery such as a coin type, a button type, and a card type. Further, the invention is not limited to the secondary battery, and can be applied to a primary battery.

[0089]

As described above, according to the negative electrode according to any one of the first to ninth aspects or the battery according to the tenth aspect, the negative electrode current collector is roughened. Therefore, the peel strength between the negative electrode current collector and the negative electrode mixture layer can be improved, and even if lithium metal is deposited on the surface of the negative electrode material during charging, the negative electrode mixture layer can be prevented from being separated. Therefore, even if charge and discharge are repeated, a decrease in capacity can be prevented, and cycle characteristics can be improved.

In particular, according to the negative electrode of claim 7, since the surface roughness of at least one surface of the negative electrode current collector is set to 0.1 μm or more, the peel strength can be sufficiently improved. Cycle characteristics can be further improved.

According to the negative electrode according to the eighth or ninth aspect, the surface roughness of the pair of surfaces of the negative electrode current collector is equal to or less than the value defined by Formula 1, or the thickness of the flat portion is equal to or more than 5 μm. As a result, the peel strength can be improved while keeping the electric resistance low, and the cycle characteristics can be further improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a secondary battery according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a part of a wound electrode body in the secondary battery shown in FIG.

FIG. 3 is a laser microscope photograph showing a surface state of a negative electrode current collector in the secondary battery shown in FIG.

FIG. 4 is a cross-sectional view illustrating a configuration of a coin cell manufactured in an example of the present invention.

FIG. 5 is a characteristic diagram illustrating a charge / discharge curve according to Example 1 of the present invention.

FIG. 6 is a characteristic diagram illustrating a charge / discharge curve according to Comparative Example 1.

FIG. 7 is a characteristic diagram illustrating a charge / discharge curve according to Comparative Example 2.

[Explanation of symbols]

11 ... battery can, 12, 13 ... insulating plate, 14 ... battery lid, 1
5 safety valve mechanism, 16 thermosensitive resistor element, 17 gasket, 20 wound electrode body, 21 positive electrode, 21a positive electrode current collector, 21b positive electrode mixture layer, 22 negative electrode, 22a negative electrode current collector , 22b ... negative electrode mixture layer, 23 ... separator, 24 ...
Center pin, 25: positive lead, 26: negative lead,
31 ... Outer can, 32 ... Positive electrode, 33 ... Outer cup, 34 ...
Negative electrode, 35 ... separator, 36 ... electrolyte, 37 ... gasket.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H017 AA03 AS02 AS10 BB16 CC01 DD01 EE01 HH03 5H029 AJ11 AK03 AL01 AL06 AL07 AL11 AL16 AM00 AM02 AM03 AM04 AM05 AM07 AM16 BJ02 CJ25 DJ07 EJ01 EJ12 HJ03 HJ04 HJ19 5CBCB CB11 CB20 CB29 DA03 DA07 FA15 HA03

Claims (10)

[Claims] 1. A negative electrode current collector having a pair of opposing surfaces and a negative electrode mixture layer capable of inserting and extracting light metal, wherein a capacity is obtained by inserting and extracting a light metal, The negative electrode is represented by the sum of a capacitance component due to precipitation and dissolution of light metal, and the negative electrode current collector is roughened. 2. The negative electrode according to claim 1, wherein the negative electrode mixture layer contains a carbon material. 3. The negative electrode according to claim 2, wherein the negative electrode mixture layer contains at least one member selected from the group consisting of graphite, graphitizable carbon, and non-graphitizable carbon. 4. The negative electrode according to claim 1, wherein said light metal includes lithium. 5. The negative electrode according to claim 4, wherein the negative electrode mixture layer contains graphite. 6. The negative electrode according to claim 1, wherein the negative electrode current collector is made of a copper foil having a roughened surface. 7. The negative electrode according to claim 1, wherein the surface roughness of at least one surface of the negative electrode current collector is 0.1 μm or more. 8. The negative electrode according to claim 1, wherein the surface roughness of the pair of surfaces of the negative electrode current collector is equal to or less than a value defined by Expression 1. ## EQU1 ## {Thickness of negative electrode current collector (μm) −5 (μm)} / N (N is 1 if only one of the pair of surfaces is roughened, and 1 2 when both surfaces are roughened.) 9. The negative electrode current collector has a flat portion having a thickness of 5 μm.
The negative electrode according to claim 1, wherein the negative electrode is at least m. 10. A battery provided with an electrolyte together with a positive electrode and a negative electrode, wherein the negative electrode has a negative electrode current collector having a pair of opposing surfaces,
A negative electrode mixture layer capable of occluding and releasing light metal, the capacity of the negative electrode is represented by the sum of a capacity component due to occlusion and release of light metal, and a capacity component due to precipitation and dissolution of light metal, The battery wherein the negative electrode current collector is roughened.