JP3051468B2 - Sheet-shaped negative electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sheet-shaped negative electrode.

2. Description of the Related Art In recent years, lithium secondary batteries have attracted attention as chargeable and dischargeable high energy density batteries. When metallic lithium is used as the negative electrode active material of this lithium secondary battery, there are problems such as the generation of dendrites and the loss of active moss-like lithium at the battery negative electrode due to charge and discharge. Therefore, studies on the negative electrode material have been actively conducted. For example, a polymer material capable of being doped with a cation such as polyacetylene or polyparaphenylene as an anode material, or an alloy such as Li and Al has been studied. However, polymer materials have problems such as low volume energy density, unstable charge state and large self-discharge, etc.The alloy layer collapses and falls off during repeated charge / discharge, resulting in a sufficient cycle life. The fact was that it had not been done.

As means for solving this problem, Japanese Patent Application Laid-Open No. 61-2594
No. 55 proposes to improve the cycle life by using a composite of polyacetylene or polyparaphenylene and lithium or a lithium alloy. However, since this negative electrode is formed by mixing powdered lithium or a lithium alloy and a powdery polymer material and using it, it is difficult to suppress collapse and falling off of the negative electrode, and it is impossible to manufacture a sheet-shaped negative electrode. there were.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of the conventional sheet-like negative electrode under such circumstances,
It is an object of the present invention to provide a sheet-shaped negative electrode having a long cycle life.

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a composite of a Li-Al alloy and a polymer material obtained by a dehalogenation-reduction polymerization reaction is used on an aluminum or aluminum alloy. As a result, the present inventors have found that a sheet-shaped negative electrode having a long cycle life can be provided, and have reached the present invention. That is, the present invention is a sheet-shaped negative electrode in which a composite of a Li-Al alloy and a polymer material obtained by a dehalogenation-reduction polymerization reaction is provided on aluminum or an aluminum alloy.

The negative electrode of the present invention has a mechanical strength,
It is excellent in current collection efficiency and internal impedance, and by using a composite of a Li-Al alloy and a polymer material obtained by a dehalogenation-reduction polymerization reaction, the polymer material becomes an active material, Since it serves as a binder and a conductive agent for the Li-Al alloy, it is possible to completely suppress the collapse and falling of the Li-Al alloy, and provide a sheet-shaped negative electrode having a long cycle life and a high energy density. The thickness of aluminum or aluminum alloy used for the sheet negative electrode of the present invention is
It is in the form of a sheet having a thickness of 10 to 300 μm, preferably 50 to 200 μm, and various materials are used, but those having a surface crystallinity mainly having a (HOO) plane are preferred. Ten
If it is less than μm, the mechanical strength of the negative electrode is not sufficient, and if it is more than 300 μm, the produced negative electrode will be thick. Also, when aluminum or aluminum alloy having uniform crystallinity is used, not only can the laminate of the Li-Al alloy and the polymer material obtained by the dehalogenation-reduction polymerization reaction be well laminated, but also the polarization characteristics of the negative electrode are good. Things. 3000 series, 50 as aluminum alloy
A 00 series alloy can be exemplified.

Further, it is preferable that the surface of aluminum or an aluminum alloy is mechanically roughened with an abrasive or the like, or roughened by electrolytic etching. The thus roughened aluminum or aluminum alloy not only does not cause the active material to fall off, but also realizes a negative electrode excellent in current collection efficiency and internal impedance. As the polymer material constituting the sheet-shaped negative electrode of the present invention, a polymer material obtained by a dehalogenation-reduction polymerization reaction is used. As a polymer material

[0005]

Embedded image (Wherein X is Cl and Br; n is 2 or 3), and a halogen derivative of quinoline chemically or electrochemically dehalogenated and reduced and polymerized is used. Such a polymer material can be synthesized by using an oxidative polymerization reaction without using a dehalogenation-reduction polymerization reaction, but the polymer material obtained by the dehalogenation-reduction polymerization reaction should be used immediately for the negative electrode. When used for a negative electrode, the process is not only simple, but also stable to cation doping (charging), and the polymer material obtained by the oxidative polymerization reaction has a cycle life. It can be much longer.

The method of synthesizing the polymer material used for the sheet-shaped negative electrode of the present invention is carried out by a chemical or electrochemical method. According to the chemical method, it is possible to synthesize a large amount of a polymer material as a powder at one time. After synthesis, it can be used as an electrode by coating with an appropriate solvent or kneading and molding with a binder. According to the electrochemical method, the monomer and the electrolyte are dissolved in an appropriate solvent, and a polymer material can be synthesized in a film form on the electrolytic electrode by cathodic reduction. The method for obtaining the sheet-like negative electrode of the present invention includes (1) a method of forming a laminate of Al and Li-Al and then coating a polymer material by an electrochemical method, and (2) chemically polymerizing on Al. After laminating the polymer material, or laminating the polymer material on Al by electrochemical method, Li is electrochemically or physically laminated,
A method of obtaining a negative electrode by performing an alloying treatment, (3) A
A method of obtaining a composite of a Li-Al alloy and a polymer material on Al by electrolyzing an electrolytic solution containing the above-mentioned monomer and Li ion using l as an electrode for electrolysis can be exemplified. The thickness of the composite of the polymer material obtained by the Li-Al alloy and the dehalogenation reduction reaction of the sheet-shaped negative electrode of the present invention is 25 to 25.
0 μm, preferably 50-200 μm. If it is less than 25 μm, the energy capacity is not sufficient, and if it exceeds 250 μm, the negative electrode becomes thick, and the mechanical strength becomes insufficient. The negative electrode of the present invention can be applied to various electrochemical devices, but exhibits excellent performance as a negative electrode for a non-aqueous secondary battery.

[0007] A lithium secondary battery can be made by using the negative electrode of the present invention. The basic structure of this lithium secondary battery is composed of the negative electrode, the positive electrode and an electrolytic solution, and if necessary, a separator and a solid electrolyte. Can be used. As the non-aqueous electrolyte, a solution obtained by dissolving an electrolyte salt in a non-aqueous solvent is used. The electrolyte salt is not particularly limited as long as it is used for a normal non-aqueous electrolyte battery.
O ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSbF
₆ , LiCF ₃ SO ₃ , CF ₃ COLi, NaClO ₄ , N
aBF ₄ , NaSCN, KBF ₄ , (Bu) ₄ NBF ₄ , (Et) ₄ −
One or more salts such as NBF ₄ , (Bu) ₄ NClO ₄ and (Bu) ₄ NClO ₄ can be used. In the combination with the present negative electrode, LiClO ₄ and CF ₃ SO ₃ Li are particularly preferable, and the charge / discharge efficiency can be drastically increased. Examples of the non-aqueous solvent include propylene carbonate, γ-butyl lactone, ethylene carbonate, sulfolane, dioxolan, tetrahydrofuran, 2methyltetrahydrofuran, dimethyl sulfoxide, and 1,2-dimethoxyethane, 1,2-ethoxymethoxyethane, methyldiglyme, Methyl triglyme, methyl tetraglyme, ethyl glyme, ethyl diglyme, butyl diglyme can be exemplified, but propylene carbonate, γ
A combination of -butyl lactone and or glymes is most preferable in terms of electric conductivity and solubility of the inorganic salt, and in combination with the present negative electrode, a solvent composition mainly composed of γ-butyl lactone enhances the charge / discharge efficiency. Particularly preferred. The concentration of the electrolyte salt is 0.5M to 7M, preferably 1M to 5M.

The positive electrode active material for a battery according to the present invention includes TiS ₂ , Nb ₃ S ₄ , MoS ₂ , Mo ₃ S ₄ , Co
Examples include chalcogenite compounds such as S ₂ , FeS ₂ , V ₂ O ₅ , Cr ₂ O ₅ , MnO ₂ , and CoO ₂ , and conductive polymers such as polyaniline, polypyrrole, poly (3-methylthiophene), and polydiphenylbenzine. In a polymer active material, it is necessary to dissolve the electrolyte in the electrolytic solution so as to correspond to the doping amount, and it is desired that the electrolyte has a high concentration and a high liquid content. As the separator, a separator having low resistance to ion movement of the electrolyte solution and excellent in solution retention is used. For example, a glass fiber filter: a polymer pore filter such as polyester, Teflon, polyflon and polypropylene; a nonwoven fabric; In addition, a solid electrolyte can be used as an alternative to the separator electrolyte.
l, AgBr, AgI, metal halides such as LiI, RbAg ₄ I ₃ ,
RbAg ₄ I ₃ CN and the like. Further, in the organic system, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polyacrylamide, etc. as a polymer matrix, the above-mentioned electrolyte salt is dissolved in the polymer matrix, or a composite thereof, or a crosslinked body thereof, a low molecular weight polyethylene oxide, A polymer electrolyte in which an ion dissociating group such as a crown ether is grafted to a polymer main chain or a viscoelastic solid electrolyte in which an electrolytic solution is contained in a high molecular weight polymer is exemplified. A combination with an electrolyte is preferable, and is preferable in preventing collapse of the negative electrode, falling off of the alloy layer, and the like, or reducing contact resistance between the negative electrode and the solid electrolyte.

[0009]

EXAMPLE 1 An aluminum foil having a thickness of 75 μm was electrochemically etched to form an infinite number of pits in a direction perpendicular to the surface. After depositing 20 μm of Li on this aluminum, a heat treatment was performed at 150 ° C. for 20 seconds to alloy the Al surface. Using this aluminum as the negative electrode and platinum as the positive electrode, 0.1 M tetrabutylammonium perchlorate, 50 mM tetrachloroxylidene CHCl ₂ C
₆ H ₄ propylene carbonate solution containing CHCl ^₂ 10mA / cm ₂
At 5 c / cm ² to produce a sheet-shaped negative electrode. Example 2 A propylene carbonate solution containing 0.1 M of tetrabutylammonium perchlorate and 50 mM of CHCl ₂ C ₆ H ₄ CHCl ₂ was used as a negative electrode and a positive electrode with platinum having countless pits formed in Example 1 at 10 mA / cm. ² was used to conduct 7 c / cm ² electrolysis. Li on this aluminum / polyphenylene vinylene electrode
After laminating 20 μm, heat treatment was performed at 150 ° C. for 20 seconds to produce a sheet negative electrode.

Comparative Example 1 After 20 μm of Li was laminated on aluminum used in Example 2, 1
Heat treatment was performed at 50 ° C. for 20 seconds to produce a sheet-shaped negative electrode. Negative electrode performance test 1 mA / c in 3M LiBF ₄ / propylene carbonate + dimethoxyethane (1: 1 volume ratio) using the negative electrodes produced in Examples 1 and 2 and Comparative Example as a working electrode and Li as a counter electrode and a reference electrode.
Charge and discharge of 1 mAh / cm ² were performed at a constant current of m ² , and the cycle life of the negative electrode was measured. Table 1 shows the results.

[Table 1]

[0011]

As described above, the sheet-shaped negative electrode of the present invention has a long cycle life and can contribute to improvement of practical performance of, for example, a secondary battery.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/60 H01M 10/40

Claims (2)

(57) [Claims] 1. A sheet-like negative electrode comprising a composite of a Li-Al alloy and a polymer material obtained by a dehalogenation-reduction polymerization reaction provided on aluminum or an aluminum alloy. 2. The sheet negative electrode according to claim 1, wherein the surface of the aluminum or aluminum alloy is roughened.