JPH04215246A - Sheet-shaped negative electrode - Google Patents

Abstract

PURPOSE:To extend the cycle life of a sheet-shaped negative electrode by providing a composition body of a Li-Al alloy and a polymer material made by the de-halogenation reduction polymerization reaction on aluminum or an aluminum alloy. CONSTITUTION:An aluminum foil with the thickness 75mum is electrochemically etched to form numerous pits in the perpendicular direction to the plane, Li with the thickness 20mum is deposited, then it is heat-treated for 20sec to 150 deg.C to alloy the surface. This aluminum is used as a negative electrode, platinum is used as a positive electrode, and a propylene carbonate solution containing 0.1M tetrabutyl ammonium perchlorate and 50mM tetrachloroxylidine is electrolyzed at 5c/cm<2> with 10mA/cm<2> to obtain the sheet-shaped negative electrode. A current collector is made of aluminum and has excellent mechanical strength, current collection efficiency and internal impedance, and a composition body with a polymer material can completely suppress the collapse and dropping of a Li-Al alloy.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet negative electrode.

BACKGROUND OF THE INVENTION In recent years, lithium secondary batteries have attracted attention as high energy density batteries that can be charged and discharged. When metallic lithium is used as the negative electrode active material of this lithium secondary battery, there are problems such as the formation of dendrites at the battery negative electrode and the precipitation of moss-like lithium that has lost its activity during charging and discharging. Therefore, negative electrode materials are being actively studied. For example, cation-doped polymeric materials such as polyacetylene and polyparaphenylene, or alloys of Li and Al are being investigated as negative electrode materials. However, polymer materials have problems such as low volumetric energy density, unstable charging state, and large self-discharge, and alloys have problems such as disintegration and falling off of the alloy layer as they are repeatedly charged and discharged, resulting in insufficient cycle life. The reality was that it was not.

[0002] As a means to solve this problem, Japanese Patent Laid-Open No. 61-2
No. 59455 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 made by mixing powdered lithium or lithium alloy with powdered polymer material and molding it, it is difficult to prevent the negative electrode from collapsing or falling off.
Furthermore, it was impossible to produce a sheet-like negative electrode.

SUMMARY OF THE INVENTION Under these circumstances, the present invention solves the above-mentioned drawbacks of the conventional sheet-like negative electrode, and
The purpose is to provide a sheet-like negative electrode with a long cycle life.

[Means for Solving the Problems] As a result of extensive studies, the present inventors used a composite of a Li-Al alloy and a polymer material obtained by a dehalogenation reduction polymerization reaction on aluminum or an aluminum alloy. The present inventors have discovered that a sheet-like negative electrode with a long cycle life can be provided by this method, leading to the present invention. That is, the present invention is a sheet-like 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.

[0003] Since the aluminum or aluminum alloy part of this negative electrode serves as a current collector, the mechanical strength of the negative electrode is low.
It is excellent in terms of current collection efficiency and internal impedance, and by using a composite of a Li-Al alloy and a polymer material obtained by dehalogenation reduction polymerization reaction, the polymer material not only becomes an active material. Since it acts as a binder and a conductive agent for the Li-Al alloy, it can completely suppress the collapse and falling off of the Li-Al alloy, and provide a sheet-like negative electrode with a long cycle life and high energy density. The aluminum or aluminum alloy used in the sheet negative electrode of the present invention is a sheet with a thickness of 10 to 300 μm, preferably 50 to 200 μm, and various materials may be used, but preferably the surface crystallinity is ( Preferably, those having mainly HOO) planes are preferable. If the thickness is less than 10 μm, the mechanical strength of the negative electrode will be insufficient, and if it is more than 300 μm, the negative electrode produced will be thick. Furthermore, if aluminum or aluminum alloy with uniform crystallinity is used, not only can the composite of the Li-Al alloy and the polymer material obtained by the dehalogenation reduction polymerization reaction be laminated well, but also the polarization characteristics of the negative electrode are good. can be taken as a thing. Examples of aluminum alloys include 3000 series and 5000 series alloys.

Furthermore, the surface of aluminum or aluminum alloy is preferably roughened by mechanical roughening using an abrasive or the like or by electrolytic etching. Aluminum or aluminum alloy whose surface has been roughened in this manner not only prevents the active material from falling off, but also makes it possible to realize a negative electrode that is excellent in terms of current collection efficiency and internal impedance. As the polymer material constituting the sheet-like 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 (In the above formula, X is Cl, Br; n is 2 or 3), and a halogen derivative of quinoline which is chemically or electrochemically dehalogenated and reductively polymerized is used. Such polymer materials can be produced without using dehalogenation reduction polymerization reactions.
Although it can be synthesized by using an oxidative polymerization reaction, the polymer material obtained by a dehalogenation reduction polymerization reaction is obtained in a state that can be used immediately for the negative electrode, so if it is used for the negative electrode, a processing step is required. Not only is it convenient, but it is also stable against cation doping (charging), and its cycle life can be significantly longer than that of polymeric materials obtained through oxidative polymerization reactions.

The polymer material used in the sheet negative electrode of the present invention can be synthesized by chemical or electrochemical methods. According to chemical methods, it is possible to synthesize large amounts of polymeric materials in the form of powder at one time. After synthesis, it can be used as an electrode by coating with a suitable solvent or kneading and molding with a binder. According to the electrochemical method, the above monomer and electrolyte are dissolved in a suitable solvent, and a polymer material can be synthesized in the form of a film on an electrolytic electrode by cathodic reduction. Methods for obtaining the sheet-like negative electrode of the present invention include (1) a method in which a laminate of Al and Li-Al is prepared and then coated with a polymer material by an electrochemical method; (2) a method in which a polymer material is chemically polymerized on Al; (3) A method of obtaining a negative electrode by laminating a polymer material on Al, or laminating a polymer material on Al using an electrochemical method, then electrochemically or physically layering Li, and performing an alloying treatment. Al
An example of a method is to electrolyze an electrolytic solution containing the monomer and Li ions using the above as an electrode for electrolysis to obtain a composite of a Li-Al alloy and a polymer material on Al. The thickness of the composite of the Li-Al alloy of the sheet-like negative electrode of the present invention and the polymer material obtained by the dehalogenation reduction reaction is 25 to 2.
It is 50 μm, preferably 50 to 200 μm. 25μ
If it is less than 250μ, the energy capacity is insufficient.
If it exceeds m, the negative electrode becomes thick and its mechanical strength becomes insufficient. The negative electrode of the present invention can be applied to various electrochemical devices, and exhibits excellent performance as a negative electrode for non-aqueous secondary batteries.

[0007] The negative electrode of the present invention can be used to make a lithium secondary battery, and the basic structure of this lithium secondary battery consists of the negative electrode, positive electrode, and electrolyte, and a separator and a solid electrolyte are added as necessary. Can be used. The non-aqueous electrolyte used is an electrolyte salt dissolved in a non-aqueous solvent, and the electrolyte salt is not particularly limited as long as it is used in normal non-aqueous electrolyte batteries, but for example, LiClO4
, LiBF4, LiAsF6, LiPF6, LiSbF
6, LiCF3SO3, CF3COLi, NaClO4
, NaBF4, NaSCN, KBF4, (Bu)4
NBF4, (Et)4-NBF4, (Bu)4NClO
4. One or more salts such as (Bu)4NClO4 can be used. In combination with the present negative electrode, LiClO4 and CF3SO3Li are particularly preferred since they can dramatically increase charge/discharge efficiency. Examples of non-aqueous solvents include propylene carbonate, γ-butyl lactone, ethylene carbonate, sulfolane, dioxolane, tetrahydrofuran, 2methyltetrahydrofuran, dimethylsulfoxide, and 1,2-dimethoxyethane, 1,2-ethoxymethoxyethane, methyl diglyme, Examples include methyl triglyme, methyl tetraglyme, ethyl glyme, ethyl diglyme, and butyl diglyme, but propylene carbonate, γ-
A combination of butyllactone and/or glymes is most preferable in terms of electrical conductivity and solubility of inorganic salts, and in combination with this negative electrode, a solvent composition mainly composed of γ-butyllactone is particularly effective in increasing charge/discharge efficiency. preferable. The concentration of the electrolyte salt is 0.5M to 7M, preferably 1M to 5M.

[0008] As the positive electrode active material for batteries in the present invention, TiS2, Nb3S4, MoS2, Mo3S4, Co
S2, FeS2, V2O5, Cr2O5, MnO2, C
Examples include chalcogenite compounds such as oO2, and conductive polymers such as polyaniline, polypyrrole, poly3-methylthiophene, and polydiphenylbenzine. In the case of a polymer active material, it is necessary to dissolve the electrolyte in the electrolytic solution in an amount equivalent to the amount of doping, and it is desirable that the electrolyte be highly concentrated and have a high content. As a separator,
has low resistance to ion movement in the electrolyte solution, and
A material with excellent solution retention is used. For example, glass fiber filters: polymer pore filters such as polyester, Teflon, polyflon, polypropylene, etc., nonwoven fabrics, or mixed paper made of glass fibers and these polymers can be used. Further, a solid electrolyte can be used in place of the separator electrolyte, and examples of inorganic electrolytes include metal halides such as AgCl, AgBr, AgI, and LiI, RbAg4I3, RbAg4I3CN, and the like. In addition, organic types include polyethylene oxide, polypropylene oxide, polyvinylidene fluoride,
Composites in which polyacrylamide or the like is used as a polymer matrix and the electrolyte salt mentioned above is dissolved in the polymer matrix, or crosslinked products of these, or in which ionic dissociative groups such as low molecular weight polyethylene oxide or crown ether are grafted onto the polymer main chain. A polymer electrolyte or a viscoelastic solid electrolyte in which an electrolytic solution is contained in a high molecular weight polymer may be used, but it is particularly preferable to use the negative electrode of the present invention in combination with a viscoelastic solid electrolyte, so that the negative electrode may collapse and the alloy layer may fall off. This is preferable in terms of preventing such problems or reducing contact resistance between the negative electrode and the solid electrolyte.

[0009]

Examples Example 1 An aluminum foil having a thickness of 75 μm was electrochemically etched to form numerous pits in the direction perpendicular to the surface. After evaporating 20 μm of Li on this aluminum,
Heat treatment was performed for 20 seconds to alloy the Al surface. Using this aluminum as a negative electrode and platinum as a positive electrode, a propylene carbonate solution containing 0.1M tetrabutylammonium perchlorate and 50mM tetrachloroxylidene CHCl2C6H4CHCl2 was applied at 5c/cm at 10mA/cm2.
2 electrolysis was performed to produce a sheet negative electrode. Example 2 Aluminum with numerous pits formed in Example 1 was used as a negative electrode, and platinum was used as a positive electrode. 0.1M tetrabutylammonium perchlorate, 50mM CHCl2C6H4CHCl
A propylene carbonate solution containing 2 at 10 mA/cm
Electrolysis was carried out at 7c/cm2. After laminating 20 μm of Li on this aluminum/polyphenylene vinylene electrode, heat treatment was performed at 150° C. for 20 seconds to produce a sheet-like negative electrode.

Comparative Example After laminating Li to a thickness of 20 μm on the aluminum used in Example 2, heat treatment was performed at 150° C. for 20 seconds to produce a sheet-like negative electrode. Negative electrode performance test The negative electrodes prepared in Examples 1 and 2 and Comparative Example were used as the working electrode, and Li was used as the counter electrode and reference electrode, and the electrodes were heated at a constant rate of 1 mA/cm2 in 3M LiBF4/propylene carbonate + dimethoxyethane (1:1 volume ratio). The cycle life of the negative electrode was measured by charging and discharging with a current of 1 mAh/cm2. The results are shown in Table 1.

[Table 1]

[0011]

As explained above, the sheet-like negative electrode of the present invention has a long cycle life and can contribute to improving the practical performance of, for example, secondary batteries.

Claims (2)

[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 on aluminum or an aluminum alloy. 2. The sheet-like negative electrode according to claim 1, wherein the surface of the aluminum or aluminum alloy is roughened.