JPS6229076A - Secondary cell - Google Patents

Abstract

PURPOSE:To obtain a secondary cell high in energy density and charging and discharge efficiency and low in self-discharge ratio, by making a negative electrode of a complex body comprising a lithium-aluminum alloy and a binder, to prevent the negative electrode from collapsing. CONSTITUTION:A positive electrode is made of an aniline polymer. A negative electrode is made of a complex body comprising a lithium-aluminum alloy and a binder. The composition ratio of the lithium of the lithium-aluminum alloy to the aluminum thereof ranges from 40:60 to 90:10. The alloy is pulverized by a ball mill or the like and graded so that the pulverized powder of 200-300 mesh in grain size is dried under reduced pressure at a temperature of 200-400 deg.C. The binder is an ethylene tetrafluoride resin, an ethylene tetrafluoride and propylene hexafluoride resin, a vinylidene fluoride resin or the like. The lithium-aluminum alloy and the binder are uniformly mixed together and filled in a die. The mixture in the die is press-molded at the room temperature or near the melting point of the binder. As for the press-molding at the room temperature, the mixture is heated near the melting point of the binder after the press-molding. The complex body is thus manufactured.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a high-performance secondary battery with high energy density, low self-discharge rate, and high charge-discharge efficiency, in which collapse of the negative electrode during charging and discharging is prevented. Regarding the next battery.

[Prior Art and Problems to be Solved by the Invention] Currently, commonly used secondary batteries include lead-acid batteries, nickel-cadmium batteries, and the like. These secondary batteries have a single cell battery voltage of about 2.0V, and are generally aqueous batteries.

In recent years, research has been actively conducted on secondary batteries that can achieve high battery voltage by using lithium as the negative electrode and conductive polymers, interlayer compounds, inorganic oxides, etc. as the positive electrode. In particular, a secondary battery using a conductive polymer as a positive electrode and lithium as a negative electrode has no hope as a high energy density secondary N battery.

As the conductive polymer used as the positive electrode of the above-mentioned battery, conductive polymers having a conjugated double bond in the main chain such as polyacetylene, polythiophene, polyparaphenylene, and polypyrrole are known [J. H.Curfman.

J. Double Kaufer, N. J. Heeger, Earl Kerner, N. G. McDiarmid, Physics Review, 821, p. 2327 (1982)
), (J, H, Kaufman, J, W, Kaw
fer.

A., J., Heeger, R., Kaner, A.
G, HacD arm id, phys, R
ev, .

B:≧-(J, 2327 (1982)>
).

In addition, there has already been a proposal to use polyaniline obtained by oxidative polymerization of aniline as a positive electrode for aqueous or non-aqueous batteries [N.G. MacDiamide et al., Polymer Preprints, Vol. 25, Iori 2. 24th
8 pages (1984) < A, G, HacDiarm
id etc., POIVgler, PreprintS, 25
．． Ik2, 248 (1984) >, Sasaki et al., Proceedings of the 50th Conference of the Electrochemical Society, p. 123 (198
3 years), Proceedings of the 51st Electrochemical Society of Japan, p. 228 (
1984)].

Among these electrically conductive polymers, it is most preferable to use polyaniline as the positive electrode in view of its high energy density, low self-discharge rate, high charge/discharge efficiency, long cycle life, etc. However, when carrying out a secondary battery reaction using lithium as a negative electrode active material and polyaniline as a positive electrode active material, dendrites are formed when lithium ions are reduced to lithium metal during charging, resulting in a decrease in charge/discharge efficiency and Positive
There are problems such as shorting of the negative electrode. Therefore, many technological developments have been reported to prevent dendrites and improve the charge/discharge efficiency and cycle life of negative electrodes. M Abraham et al. “Lithium Batches”.

Edited by J.P. Kalbuff 1, published by Academic Press, London (1983) <K, H, Abraham
am etat, in″Lithium Batte
ries”, J, P, Gabano.

edito, l, academic press, l
Ondon (1983) > ), a method of preventing lithium dendrites by adding additives to the electrolyte system or alloying the electrode itself with aluminum [Japanese Patent Application Laid-open No. 108281/1983] has been proposed. There is. However, with the above method, not only is the dendrite improvement effect not necessarily satisfactory, but when a lithium-aluminum alloy is used for the electrode, the alloy electrode collapses and the performance as a battery cannot be maintained. there were.

It has also been proposed to use a solid solution of silver and an alkali metal as a negative electrode (Japanese Unexamined Patent Publication No. 73860/1983).

In this case, there is no collapse like in the alloy of lithium and aluminum, but the amount of alkali metal that alloys quickly enough is small, and the metallic alkali metal may precipitate without being alloyed. To prevent this, The use of porous materials is recommended. Therefore, the charging efficiency of large currents is poor, and alloys with a high alkali metal ratio gradually accelerate the refinement due to charging and discharging, leading to problems such as a rapid decrease in cycle life, high energy density, and low self-discharge rate. However, a secondary battery with high charge/discharge efficiency and long cycle life has not been obtained. .

[Means for Solving the Problems] As a result of various studies in order to solve the drawbacks of the above-mentioned conventional techniques, the present inventors found that by using a composite consisting of a lithium-aluminum alloy and a binder for the negative electrode, The present inventors have discovered that a lithium-aluminum alloy does not disintegrate during charging and discharging, and that a high-performance secondary battery can be obtained, leading to the completion of the present invention.

That is, the present invention relates to a secondary battery characterized by using an aniline polymer for the positive electrode and a composite consisting of a lithium-aluminum alloy and a binder for the negative electrode.

The composite used as a negative electrode in the present invention means a molded body made from a mixture of a lithium-aluminum alloy and a binder.

The lithium-aluminum alloy used as one of the constituent elements of the negative electrode in the present invention can have an elemental composition ratio of lithium and aluminum ranging from 10+90 to 90:10, but in practical terms, lithium in aluminum is It is preferable to use a ratio of 40:60 to 90:10, which provides a high diffusion rate. The lithium-aluminum alloy is ground into powder using a ball mill, etc., and then
A powder with a mesh size of 50 to 500, preferably 200 to 300, obtained by classifying with a sieve, etc., is sieved under reduced pressure to
It is preferable to use it after drying at a temperature of 0 to 400°C. The above heat treatment removes impurities on the surface of the alloy powder and improves its adhesion to the binder when mixed with the binder.

The binder used as the other component of the negative electrode of the present invention is an organic solvent and is inert to the electrolyte, and does not have any reactivity with the lithium-aluminum alloy. Preferably something with no objects. Such binders include tetrafluoroethylene resin, tetrafluoroethylene-hexafluoropropylene resin, vinylidene fluoride resin, and the like, and among these, tetrafluoroethylene resin is preferred. can. Two or more of these binders may be used in combination.

The blending amount of the binder is 1% to 50% by weight, preferably 5% to 2% by weight based on the lithium-aluminum alloy.
It is 0% by weight. If the binder content is less than 1% by weight,
If the disintegration effect of lithium aluminum alloy is not sufficiently improved during charging and discharging, and the amount of -5 binder is more than 50% by weight, the binder will rise to the surface and affect the energy density and electrical conductivity. This has the disadvantage that the battery performance deteriorates due to a decrease in energy consumption.

One example is a method in which a lithium-aluminum alloy and a binder are mixed, the mixture is then filled into an electrode-shaped mold, and the mixture is molded by applying pressure at room temperature. The pressure to be applied at this time varies depending on the filling amount of the mixture, etc., so it cannot be determined unconditionally, but it is generally 0.2 t/c, 2 to 5 t/c.
/cm2 is good, and the most preferable pressure range is 0.5t/n
2 to 1. Ot/α2.

The composite molded as described above can sufficiently exhibit the effects of the present invention even when used as a negative electrode as it is, but when molding the composite, it is necessary to heat and pressure mold it near the melting point of the binder.
Alternatively, if a mixture consisting of a lithium-aluminum alloy and a binder is pressure-formed and then heat-treated near the melting point of the binder, the degree of bonding between the lithium-aluminum alloy and the binder will further increase, and the electrode strength will also become stronger. , and has the advantage of being less likely to disintegrate than an untreated product that is not heat-treated near the melting point of the binder. The heating time at this time is 1 minute to 60 minutes, as long-term heating will melt the binder too much and cover the entire surface of the alloy powder with the binder, making it impossible for lithium to move. minutes, preferably 2 to 15 minutes
Minutes of time is preferred.

In addition, since lithium-aluminum alloy is extremely reactive to moisture, oxygen, nitrogen, etc., operations such as crushing, mixing, molding, and heating are preferably performed under an inert gas atmosphere or vacuum. The polymer is made by reacting aniline monomers with oxidizing agents such as ammonium persulfate and hydrogen peroxide.
Manufactured by any of the following methods: chemical polymerization method in which an electrode is placed in an acidic aqueous solution of an aniline monomer, and aniline polymer is oxidized and precipitated on the positive electrode by energization. But that's fine.

Representative examples of aniline monomers include aniline, 2-
Methoxyaniline, 3-methoxyaniline, 2,3-dimethoxyaniline, 2,5-dimethoxyaniline, 2,
6-dimethoxyaniline, 3,5-dimethoxyaniline, 2-ethoxy-3-methoxyaniline, 2,5-diphenylaniline, 2-phenyl-3-methylaniline,
Examples include 2,3.5-trimethoxyaniline, 2.3-dimethylaniline, 2,3.5.6-titramethylaniline, and among these, aniline is preferred. Specific methods for producing aniline polymers are described in, for example, N.G. Green and N.E. Woodhard, Journal of Chemical Fusaiati 1. 9th
Volume 7 (1910), page 2388, volume 101 (1)
913), p. 1117; Ni Kitani and J.
Izumi et al.; Britin Chemical Society of...
Japan, Volume 57 (1984), Illustration, 8. 225th
It is described on page 4.

The aniline polymer produced by the above method is often obtained in a form containing moisture, impurities, etc., and if used as a positive electrode as is, these moisture and impurities will have a negative effect on battery performance. In particular, since it is highly reactive with lithium, there is a risk that the self-discharge rate and number of cycles may be reduced. Therefore, it is preferable to wash and dry the aniline polymer to remove moisture, impurities, etc. before use.

The solvent for the electrolytic solution used in the secondary battery of the present invention is preferably aprotic and has a high dielectric constant. For example, ethers, ketones, amides, sulfur compounds, phosphate ester compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds, sulfolanes, etc. can be used, but among these, ethers , ketones, phosphate ester compounds, chlorinated hydrocarbons, carbonates, and sulfolanes are preferred. Representative examples of these solvents include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, monoglyme, 4-
Methyl-2-pentanone, 1゜2-dichloroethane, γ
-butyrolactone, valerolactone, dimethoxyethane, methylformate, propylene carbonate, ethylene carbonate, dimethylformamide, dimethylsulfoxide, dimethylthioformamide, ethyl phosphate, methyl phosphate, chlorobenzene, sulfolane, 3-methylsulfolane, etc. can.

These solvents can also be used in combination of two or more.

Further, specific examples of the supporting electrolyte used in the secondary battery of the present invention include Li PFe and Li Sb Fa.

Li C104, Li As Fa, CF3803
Li.

Li BF4, Li 8 (81) 4.

Examples include Li B (Et)2 (8U)2, but the present invention is not necessarily limited to these. These supporting electrolytes may be used alone or in combination of two or more.

The supporting electrolyte cannot be unconditionally defined as it varies depending on the type of aniline polymer used in the positive electrode, the type of cathode, charging conditions, operating temperature, type of supporting electrolyte, type of solvent, etc., but in general 0.5-10 mol/
It is preferable that it is within the range of g. The electrolyte may be homogeneous or heterogeneous.

In the secondary battery of the present invention, the amount of dopant doped into the aniline polymer is 10 to 180 mol%, preferably 20 to 100 mol%, based on 1 mol of repeating units of the aniline polymer. It is.

In lithium-aluminum alloys, it is advantageous to increase the utilization rate of lithium because it increases the energy density, but if all lithium is used, dendrites are more likely to occur, so the utilization rate is between 10% and 90%. It is preferable to perform charging and discharging at

The dope world and lithium usage rate are based on the amount of electricity flowing during charging.
can be freely controlled by measuring.

It may be carried out either under constant current, constant voltage, or under varying conditions of current and voltage.

[Example] Next, Examples and Comparative Examples will be given to demonstrate the present invention.While mechanically stirring a 1N aqueous solution of hydrochloric acid having an aniline concentration of 0.22 mol/g, the liquid temperature was raised to 40°C. It was heated externally to maintain it. When ammonium persulfate ((NH4) 2320 g) equivalent to 0.25 mol/1 was gradually added to the liquid as an oxidizing agent, polyaniline crystals were precipitated in the liquid. After the addition of ammonium persulfate was completed, the temperature was maintained at 40° C. for 3 hours to complete the reaction. The obtained polyaniline was a powdery green-black crystal. The crystals were filtered, washed with a large amount of pure water, and then neutralized with aqueous ammonia. After that, water washing was performed again. Next, it was dried at 80° C. under reduced pressure for 5 hours until moisture disappeared.

A positive electrode was prepared by filling 34 gtg of dried polyaniline into a 10 Mφ mold and press-molding it at room temperature.

(Preparation of Negative Electrode) A lithium-aluminum alloy with an elemental composition ratio of 50:50 manufactured by Suido Metal Co., Ltd. was ground for 1 hour using a ball mill. The obtained lithium-aluminum alloy powder was
The powder was classified using a 0 to 300 mesh sieve, and the powder was heated to 350°C under reduced pressure and dried for 1 hour.

The polytetrafluoroethylene resin used as a binder was obtained by separating the polytetrafluoroethylene resin powder (1) from an aqueous dispersion solution manufactured by Daikin Industries, Ltd., and then drying it under vacuum at 150°C.

The lithium-aluminum alloy powder obtained by the above treatment and the tetrafluoroethylene resin powder were mixed at a weight ratio of 90 parts of the alloy powder to 1 part of the resin powder, and the mixture was mixed in a tumbler mixer for 2 hours. They were mixed to homogenize the alloy powder and resin powder. 10.35 mg of mixed powder. The mixture was filled into a mold with diameters of ., . . . , . . Next, the obtained molded body was heat treated at 320° C. for 10 minutes. The molded negative electrode has a thickness of 450 μm,
The density was 1.1 sh/cttr3.

<Configuration of experimental cell> Positive electrode (polyaniline) produced by the above method; negative electrode (lithium-aluminum alloy and lithium boroborofluoride equivalent to ethyl tetrafluoride in a volume ratio of propylene carbonate and 1.2-
It's a dimethoxyethane mixed solvent.

(Battery Performance Test) A repeated charging and discharging test was conducted under conditions where the current density for charging and discharging was set at 5 mA/cyr2, and the lower limit voltage during discharging was set at 1.0V. Charge/discharge efficiency is 97 at the 5th cycle
%, the amount of electricity at that time was 13.42 coulombs, and the utilization rate of lithium was 15%. This battery is
Even at the 200th cycle, the results were similar to the 8th cycle.
When the 201st self-discharge test was conducted for 720 hours, the self-discharge rate was 3.8%.

[Comparison Example: Instead of the composite made of lithium-aluminum alloy and tetrafluoroethylene resin used as the negative electrode in the example, it was prepared in the same manner as in the example or only a lithium-aluminum alloy was used as the negative electrode. A cycle test was conducted under the same charging and discharging conditions as in the example except for this. As a result, the charging/discharging efficiency was 93% at the fifth time. The amount of electricity that flowed at that time was 1
3.2 coulombs, lithium utilization rate is 13.7%
However, at the 150th cycle, the charge/discharge efficiency was 80.
%, and when the self-discharge rate was measured the next time,
It was 80% in 720 hours. After the experiment was completed, the battery cell was disassembled and the negative electrode was observed, and it was found that it had collapsed significantly (the electrode did not maintain its shape).

[Effects of the Invention] As described above, by using a composite made of a lithium-aluminum alloy and a binder as a negative electrode, it is possible to prevent the negative electrode made of a lithium-aluminum alloy from collapsing, and It has now become possible to obtain a secondary battery that operates with low self-discharge rate and high charge/discharge efficiency.

[Brief explanation of drawings]

The figure is a schematic cross-sectional view of a battery cell for measuring characteristics of a secondary battery, which is an integral example of the present invention. 1... Nickel lead wire for negative electrode 2... Nickel mesh current collector for fA electrode 3... Negative electrode 4... Porous polypropylene diaphragm 5... Positive electrode 6... Nickel m for positive electrode Current collector 6... Positive electrode lead I 8... Teflon container Patent applicant Showa Denko Co., Ltd. Hitachi Ltd.

Claims (5)

[Claims] (1) A secondary battery characterized by using an aniline polymer for the positive electrode and a composite consisting of a lithium-aluminum alloy and a binder for the negative electrode. (2) The secondary battery according to claim (1), wherein the composite is obtained by pressure molding a mixture comprising a lithium-aluminum alloy and a binder. (3) The secondary battery according to claim (1), wherein the composite is obtained by press-molding a mixture consisting of a lithium-aluminum alloy and a binder at a temperature near the melting point of the binder. . (4) Claim 1, wherein the composite is obtained by pressure-molding a mixture of a lithium-aluminum alloy and a binder and then heat-treating the mixture at a temperature near the melting point of the binder. Secondary battery. (5) The secondary battery according to claim (1), wherein the binder is a tetrafluoroethylene resin, a tetrafluoroethylene-hexafluoropropylene resin, a vinylidene fluoride resin, or a mixture thereof.