JPH02297867A - Secondary battery - Google Patents

Abstract

PURPOSE:To provide a secondary battery with large capacity and increased energy density by allowing the positive electrode of secondary battery to contain electrolyte in a specific wt.%. CONSTITUTION:The positive electrode of a secondary battery contains electrolyte in 35-50wt.%. Even with a thicker pos. electrode, the electrode reaction can be generated uniformly if not merely electrolyte exists inside the pos. electrode but the amount of electrolyte is ample. According to this constitution the pos. electrode contains sufficient electrolyte to perform electrode reactions, which take place uniformly over the whole pos. electrode, that should increase the rate of utilization of conductive highpolymer, enhance the energy density even it is achieved in large capacity, and also enlarge the output current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a secondary battery having a large capacity and a high energy density.

[Background Art] In recent years, as electric devices have become smaller, lighter, and thinner, there has been an increasing demand for smaller, lighter, and thinner batteries for use as power sources, and various batteries have been proposed. Among them, secondary batteries that use conductive polymer materials such as polypyrrole, polyaniline, and polyacetylene for the positive electrode and lithium for the negative electrode are attracting attention because they are lightweight and have high energy density.

In particular, polyaniline has a fibrillar morphology and a large specific surface area, so it is attracting attention as an electrode active material that can form secondary batteries with high output density, large discharge capacity, and excellent repeated charging and discharging life. .

As described above, attempts have been made to use conductive polymer materials to produce secondary batteries with large capacity and high energy density.

However, although a secondary battery of several mAh made from a thin film of conductive polymer material with a thickness of several tens of microns exhibits sufficiently excellent performance, If the above secondary battery is manufactured, the capacity of the battery will be small relative to the amount of conductive polymer material filled, the energy density will be the same as or lower than that of a NiCd battery, and the output current will be small. This was causing a problem.

There have been many attempts to fabricate high-capacity secondary batteries using conductive polymer materials; for example, Japanese Patent Application Laid-Open No. 63-28586
3 proposes stacking electrodes using thin layers of conductive polymer to improve the utilization rate of conductive polymer.
Since a large number of thin electrodes are laminated, each electrode is likely to be misaligned, resulting in disadvantages such as poor workability and a tendency for the performance of the mounted battery to deteriorate.

In addition, in JP-A-61-200548, the bulk density is 0.4 to 1.
．． A proposal has been made to reduce the amount of electrolyte used by using polyaniline adjusted to 1 g/ctn3 as an electrode, but although relatively good results can be obtained with miniature secondary batteries, it is insufficient for large-capacity secondary batteries. I couldn't get the best performance.

[Problems to be Solved by the Invention] In view of these circumstances, an object of the present invention is to provide a secondary battery with large capacity and high energy density.

[Means for Solving the Problems] The present inventors have diligently endeavored to investigate the cause of the difference between miniature secondary batteries and large-capacity secondary batteries, and have found that In miniature batteries, the thickness of the positive electrode using molecules is about a few tens of micrometers, while in large-capacity batteries it is several hundred micrometers to a few square meters, which means that in miniature batteries, the electrode reaction occurs almost uniformly across the entire positive electrode. In contrast, in large-capacity batteries, electrode reactions mainly occur only near the outside of the positive electrode, which is in contact with the electrolyte, and it has been found that electrode reactions are difficult to occur inside the positive electrode.

Based on this knowledge, the present inventors believe that if enough electrolyte exists inside the positive electrode, the electrode reaction can occur uniformly even in thick positive electrodes. As a result of further investigation, we discovered that not only the presence of an electrolytic solution inside the positive electrode but also a sufficient amount of electrolyte is necessary, leading to the present invention. That is, the present invention provides a secondary battery using a conductive polymer material as a positive electrode active material, in which the positive electrode of the secondary battery has a diameter of 35 to 5.
This is a secondary battery characterized by containing 0.2% electrolyte.

In the secondary battery of the present invention, since the positive electrode contains 35 to 50% electrolyte, the electrolyte necessary for the electrode reaction is sufficiently present inside the positive electrode, and the electrode reaction can occur uniformly throughout the positive electrode. , the utilization rate of the conductive polymer is high, and the supply of electrolyte from the outside of the positive electrode is not required, so the energy density is high and the output current can be increased. The positive electrode of the secondary battery of the present invention is an electrode using a conductive polymer, and the conductive polymer may be used alone or a conductive material and a binder may be added thereto as necessary. The electrolyte content of the positive electrode of the present invention is 35 to 50% by weight, preferably 4% by weight.
It is 0 to 50% by weight. If it is less than 35%, it is necessary to supply the electrolyte necessary for the electrode reaction from outside the positive electrode, and if it is more than 50%, it is disadvantageous in terms of the energy density of the positive electrode.

The weight of the positive electrode in the present invention refers to the positive electrode active material and the electrolyte, and the electrolyte in the present invention refers to the electrolyte anion and its electrolyte salt that are doped into the positive electrode active material as a dopant and store energy. The electrolyte may be doped into the positive electrode active material, dissolved in the electrolytic solution in the form of ions, or precipitated as an electrolyte salt, but it is necessary to always exist within the positive electrode. As an electrolyte, PFS '', 5bF6-1AsF6'',
BF'4-1C104-1SCN-1CI'''', Br-
Anions such as 1I′″ and these together with Li+, Na+,
Examples include salts such as Ka'' and (R4N)+.

Methods for containing electrolyte in the positive electrode include a method in which the positive electrode is immersed in a high concentration electrolytic solution and then gas is removed from the inside of the stopper, a method in which electrolyte salt is mixed and molded when molding the positive electrode, This can be carried out by a chemical method, an electrochemical method, or a combination of these methods.

The electrolytic solution contained in the positive electrode is preferably present in an amount of 25 to 65% by volume. If it is less than 25%, doping and dedoping reactions of the electrolyte present inside the positive electrode into the positive electrode active material cannot be carried out smoothly, and if it is more than 65%, it is disadvantageous in terms of energy density.

The conductive polymer used in the secondary battery of the present invention is required to have a certain degree of conductivity, and specifically, aniline, 4-aminodiphenylamine, N
-Methylaniline, N-ethylaniline, 4-(N-methylamino)diphenylamine, diphenylamine, O
Examples include -methylaniline, 0-ethylaniline, l-methylaniline, ethylaniline, 4-(N-ethylamino)diphenylamine, N,N'-diphenyl-p-phenylenediamine, and the like. These anilines and their derivatives can be used alone or as a mixture of two or more. However, most preferred is aniline.

The conductive polymer of the present invention can be synthesized by a chemical polymerization method or an electrolytic polymerization method. According to the electrolytic polymerization method, a conductive polymer is formed in the form of a film on an electrode for electrolysis. Examples of such conductive polymers include acetylene, virol, thiophene, aniline, benzene, diphenylbenzidine, diphenylamine, triphenylamine, azulene, and pyridine. Examples include polymers made from these or derivatives thereof, which have high electrical conductivity by doping with impurities and can store energy at the same time. The electrical conductivity of this material is such that when used in batteries, at least in a doped state! 0°5Slc112 or more, preferably 10゛1s/c+a'' or more.10-'S/c*2
If it is less than this, the internal impedance of the battery electrode becomes high, which is disadvantageous.

In particular, polyaniline compounds made from polyaniline and its derivatives have a fibrous morphology, a large surface area, and a high energy density, so they are most preferred as active materials for large-capacity, artificially produced secondary batteries. As monomers of polyaniline compounds, those represented by general formulas (I) and (n) are synthesized in a similar manner, so if this electrode is used as it is as a positive electrode for secondary batteries, it will be possible to synthesize conductive polymers as well. This is economically advantageous since a positive electrode for a secondary battery is manufactured. According to the electrolytic polymerization method, good adhesion between the conductive polymer and the electrolytic electrode (current collector) can be obtained, but in order to strengthen the adhesion, the surface of the current collector must be polished using a polishing machine. The surface is roughened by gelatinizing agent, etching, etc., and more preferably, the current collector has a roughness of 0.5 to 100.
It is preferable to improve the surface area of the current collector by providing holes with a size of 0μ-1, preferably 1 to 100μ. According to the chemical polymerization method, conductive polymers are obtained in powder form and require molding in order to be used as electrodes, but conductive polymers can be synthesized in large quantities and at low cost.

As mentioned above, the positive electrode used in the secondary battery of the present invention may be composed of a conductive polymer alone, but since the conductive polymer decreases in its electrical conductivity in a dedoped (discharged) state, it is necessary to use a conductive material. may be dispersed in the positive electrode to keep the electrical conductivity of the positive electrode constant.

A preferred method for dispersing the conductive material is to process the conductive polymer into particles, mix the conductive material and a binder, and then mold the particles. As the conductive material, carbon bodies such as carbon black and acetylene black, metals such as CuSAl and Ni,
Particles or fibers of alloys such as stainless steel are used.

The amount of conductive material used is 1 to 25 per conductive polymer.
% is preferably 2 to 15%. If it is less than 1%, it is difficult to improve the electrical conductivity of the positive electrode, and if it is more than 25%, the energy density of the positive electrode becomes small, which is disadvantageous. As the binder, a substance that is stable and has binding properties against the electrolyte, such as powder or dispersion of Teflon, polyester, polyethylene, polypropylene, etc., can be used, and the amount used is 0.5 to 20%, preferably 1
~15%. If it is less than 0.5%, the binding power will not be sufficient, and if it is more than 20%, the energy density of the positive electrode will become small, which is disadvantageous.

The secondary battery of the present invention basically includes a positive electrode, a negative electrode, and an electrolyte, and a separator may be provided between the electrodes. The electrolytic solution is composed of a solvent and an electrolyte.

As negative electrode active materials, polyacetylene, polythiophene,
Conductive polymers such as polyparaphenylene and polypyridine,
Li and AI, Mg, Pb.

An alloy of Si, Ga1, In, etc. can be used.

Although a sheet-like negative electrode active material can be used alone for the negative electrode, in order to improve the handling properties of the sheet-like negative electrode and the current collection efficiency, a composite of the above-mentioned negative electrode active material and current collector is used. Can be used.

Materials for the negative electrode current collector include Ni and AI.

Cu5PtSAu, stainless steel, etc. are preferable, and AI is more preferable from the viewpoint of weight reduction.

Conventionally, AI-LL has been used as a negative electrode to prevent dendrites, but it may also be one in which Al and Li are not alloyed.

Methods for laminating the negative electrode active material on the negative electrode current collector include methods of forming the negative electrode active material by vapor deposition or electrochemical methods, and mechanical methods such as bonding the current collector and an active material such as Li. .

In the electrochemical method, the negative electrode current collector itself may be used as an electrode to deposit Li, etc., but if the negative electrode current collector is coated with an ionic conductive polymer and then electrolytically deposited, the current collector can be deposited. - Active materials such as Li can be uniformly deposited at the interface of polymers.

Examples of the electrolyte (dopant) in the battery electrolyte include the following anions or cations:
A polymer complex doped with cations provides an n-type conductive polymer, and a polymer complex doped with anions provides a p-type conductive polymer. A polymer complex doped with anions can be used for the positive electrode, and a polymer complex doped with cations can be used for the negative electrode. As anions, PFG″″, SbF6
Halide anions of elements of the Va group such as ``'', AgF6'''', SbCI G- HBFa-BRs- (R:
Examples include halide anions of Na group elements such as phenyl and alkyl JIi), perchlorate anions such as ClO4-, and halogen anions such as Ct-1Br''' and !-.

Examples of cations include alkali metal ions such as Li'', Na'', and K'', (R4N)'' [R: carbon number 1~
Examples include 20 hydrocarbon groups 1 and the like.

Specific examples of compounds that provide the above dopants include L
iPFi, t, tsbFs, LiAsF5, LiCIO
4, NaClO4, K I 1K P F @ 1K
S b F G , K A s F G , K CI O
4, [(n-Bu) 4 Nl ”・AsF6-1[
(n-Bu), 4N] ”・ClO4″”, [(n
B u) 4 Nl ” ΦB F 4″″, LiA
Examples include lCl4, LiBF4, and the like.

The solvent constituting the electrolyte solution is not particularly limited, but a relatively highly polar solvent is preferably used. Specifically, propylene carbonate, ethylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyl lactone, dioxolane, triethyl phosphate, triethyl phosphite, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane. , dimethoxyethane, polyethylene glycol, sulfuran, dichloroethane, chlorobenzene, nitrobenzene, or a mixture of two or more organic solvents.

As the separator, one is used that has low resistance to ion movement of the electrolyte solution and has excellent solution retention. For example, glass fiber filters; polymeric bore filters such as polyester, Teflon, polyflon, and polypropylene; nonwoven fabrics; or nonwoven fabrics made of glass fibers and these polymers can be used.

Example O Manufacturing method of positive electrode active material 1 Polyaniline was synthesized on the working electrode by constant potential electrolytic polymerization method at 0.8 V vs SCE in an electrolytic cell in which 0.5 M aniline and 0.75 M sulfuric acid aqueous solution were used as a working electrode and a platinum plate as a counter electrode. After dedoping -0.4V vs SCE in a 0.2N sulfuric acid aqueous solution using a platinum-polyaniline electrode as a working electrode, it was washed with water and dried in vacuum. The polyaniline was peeled off from the platinum and ground with an agate mill to produce a positive electrode active material.

Manufacturing method 2 of O positive electrode active material 0.5M ammonium persulfate was added to a 0.5M aniline and 1M hydrochloric acid aqueous solution to synthesize polyaniline powder. This polyaniline powder was dedoped with a 20% hydrazine/methanol solution, washed with acetonitrile, and dried in vacuum to produce a positive electrode active material.

Manufacturing method 3 of O cathode active material After etching holes with a diameter of 5 μm at a rate of 100 holes/am2 on a 10 μμ thick SOS foil, #2
Blasting was performed using No. 00 emery particles at a pressure of 1 kg/cm 2 .

This was used as an electrode for electrolysis using 1M aniline, 3MI (BF4
In an aqueous solution, constant current of lsA/am 2, electrolysis! 20
Electrolytic polymerization was performed at C/cs+2. 5US - In a 0.1MHBF4 aqueous solution using a polyaniline electrode as a working electrode -
After dedoping with 0.4V vsS CE, washing with water,
Vacuum drying was performed to produce a 5US-polyaniline electrode.

Example 1 Polyaniline 0.2 manufactured by manufacturing method 1 of positive electrode active material
Using g, polyaniline l, carbon black
0.1, Teflon dispersion 0°05 mixed,
After performing pressure molding of 50 kg, vacuum drying was performed at 100° C. for 2 hours. This is 4MLiB F 4 / P C
After being immersed in the solution, it was left in a vacuum of 10-2 torr for 5 minutes to degas it, and then returned to normal pressure with argon gas and immersed in the solution for 24 hours.

Next, using Li as the negative electrode, 3.5M Li BF4 / dimethoxyethane in propylene carbonate (7:3) as the electrolyte, and a polypropylene nonwoven fabric as the separator, the test cell was heated at 5 mA/c as shown in Figure 1.
The battery characteristics were measured by charging and discharging at a constant current of m''.The electrolyte content of this positive electrode was 30%.

Example 2 A battery was manufactured in the same manner as in Example 1, except that polyaniline manufactured by positive electrode active material manufacturing method 2 was used, and battery characteristics were measured. Note that the content of the electrolyte in this positive electrode was 37%.

Example 3 Polyaniline 0.2 manufactured by manufacturing method 2 of positive electrode active material
using 1.g of polyaniline and 0.0.g of carbon black.
15, Teflon dispersion 0.05L i S
b F 60.20 was mixed, pressure molded into 60 kg, and then vacuum dried at 100° C. for 2 hours to produce a positive electrode. This positive electrode was 3.0M L i S b F 6 /
It was immersed in a propylene carbonate solution and degassed. Next, using L L -A I alloy (A120%) as the negative electrode and 3.0M LIBF4/propylene carbonate solution as the electrolyte, the test cell was heated at 5 A/
The battery characteristics were measured by charging and discharging at a constant current of c2. Note that the electrolyte content of this positive electrode was 39%.

Example 4 A 5US-polyaniline electrode (polyaniline weight 0.3g) manufactured by manufacturing method 3 of positive electrode active material was used as a 5M LiB
After immersing in F</propylene carbonate solution and degassing, it was left in the solution for 12 hours. Next, battery characteristics were determined under the same conditions as in Example 1 using 3.5 ML i BF4 /propylene carbonate as the electrolyte and lithium as the negative electrode. The electrolyte content of this positive electrode is 4
It was 5%.

Comparative Example 1 A battery was manufactured in the same manner as in Example 1, except that 250 kg of pressure molding was performed, and the battery characteristics were determined in one lung. Note that the electrolyte content of this positive electrode was 17%.

Comparative Example 2 A positive electrode was produced in the same manner as in Example 2, except that pressure molding of 100 kg was performed. The produced positive electrode is extremely brittle;
When installing the battery, the electrode broke into multiple pieces. This battery was tested for battery performance in the same manner as in Example 2. Note that the electrolyte content of this positive electrode was 52%.

Comparative Example 3 In Example 4, a 200 kg pressure press was performed.
A battery was manufactured in the same manner except that a US-polyaniline electrode was used, and the battery characteristics were measured.

Note that the electrolyte content of this positive electrode was 19%.

Battery performance test results [Effects of the invention] As explained above, the secondary battery according to the configuration of the present invention has the following effects:
It has large capacity and high energy density.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a test cell used for evaluating the characteristics of the secondary battery of the present invention. 1st block

Claims (1)

[Claims] (1) A secondary battery using a conductive polymer material as a positive electrode active material, wherein the positive electrode of the secondary battery contains 35 to 50% by weight of electrolyte.