JPH01107468A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To increase energy densities per unit volume and unit weight by using polyaniline as a positive electrode and a specified electrolyte. CONSTITUTION:In a secondary battery using polyaniline in a positive electrode 6, an electrolyte 9 prepared by dissolving LiBF4 in 1,2-dimethoxyethane is used and the concentration of the LiBF4 is made to 4-6mol/l. Although this electrolyte 9 is of high concentration, it does not decrease the charge-discharge performance of the battery, and when the concentration ot LiBF4 exceeds 4mol/l, energy density per weight is substantially increased. The concentration in which the electrolyte is liquid at room temperature is up to about 6mol/l. The amount ot the electrolyte 9 in the battery is remarkably reduced and energy densities per unit volume and unit weight are increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a lithium secondary battery using polyaniline as a positive electrode, and more particularly to improvement of its electrolyte.

[Conventional technology]

Among secondary batteries that use conductive polymers as electrode materials, lithium secondary batteries that use polyaniline as the positive electrode have the advantages of high charge/discharge efficiency, low self-discharge, and resistance to overdischarge. (For example, 24th Battery Symposium Abstracts, page 197).

However, when actually assembling a battery, despite the light weight of polyaniline, a large amount of electrolyte must be used, making it impossible to sufficiently increase the energy density per volume and weight. be.

This is because the charging and discharging reactions of this battery utilize the doping and dedoping reactions of anions in the electrolyte to polyaniline, and the anions and cations in the electrolyte play the same role as the battery active material. This is due to the need for a large amount of electrolyte.

[Problem that the invention seeks to solve]

This invention solves the problem that lithium secondary batteries using polyaniline as the positive electrode require the use of a large amount of electrolyte, and thereby enables lithium secondary batteries with high energy density per volume and weight. The purpose is to provide.

[Means for Solving the Problems] In order to achieve the above object, the present inventors have made extensive efforts to develop an organic electrolyte system capable of dissolving a large amount of lithium salt in a lithium secondary battery using polyaniline as a positive electrode. As a result of repeated studies, we found that when LiBF4 is dissolved in 1,2-dimethoxyethane, LiBFa can be dissolved at a high concentration of 4 mol/1 or more, and even at such a high concentration, there will be no hindrance to the battery reaction. They discovered that even if the amount of electrolyte injected into the battery is reduced, the predetermined discharge capacity can be maintained and the energy density per volume and weight of the battery can be increased, and this led to the completion of the present invention. Ta.

In other words, conventionally, inorganic positive electrode active materials such as titanium disulfide (TiS) have been mainly used in lithium secondary batteries, so the electrolyte only needs to ionically conduct lithium ions to the positive electrode side. Therefore, about 1 mol/I! of lithium salt! Generally, an electrolytic solution with a lithium salt concentration of about 1 mol/l is used when polyaniline is used for the positive electrode, as is the case when using an inorganic positive electrode active material such as titanium disulfide. However, as mentioned above, LiBF is 4 mol/I! .

By using the electrolyte dissolved above, the amount of electrolyte in the battery can be significantly reduced, and a small and lightweight lithium secondary battery with high energy density per volume and weight can be produced. Furthermore, in a lithium secondary battery using polyaniline as a positive electrode, even such a high solute concentration in the electrolytic solution does not cause any hindrance to the battery reaction.

Furthermore, the electrolytic solution prepared by dissolving LiBF4 in 1,2-dimethoxyethane does not deteriorate the charge-discharge cycle characteristics of the battery even at a high LtBFn concentration of 4 mol/It or more, and therefore, the electrolytic solution that polyaniline has It is possible to produce a lithium secondary battery that takes advantage of its good discharge cycle characteristics.

In the present invention, the LiBF4 concentration in the electrolyte is 4 mol/
The amount is adjusted to 1 to 6 mol/l for the following reasons. As the concentration of LiBF increases, the energy density per volume and weight of the battery increases (However, when the LiBF4 concentration becomes 4 mol/1 or more, the LiBF* concentration increases
The energy density per volume and weight is significantly improved compared to those with a size of about 1. Even if the LiBFa concentration exceeds 4 mol/Il, the effect of improving the energy density per volume and weight of the battery does not change much compared to when the LiBF4 concentration is 4 mol/l, and the liquid state at room temperature does not change much. This is because the concentration that can be maintained is up to about 6 mol/l.

In order to use polyaniline for a positive electrode, polyaniline powder is usually pressure-molded into a pellet shape or formed into a sheet shape. At that time, a binder such as polytetrafluoroethylene may be added to the polyaniline.

Lithium or a lithium alloy is used for the negative electrode. Examples of the above-mentioned lithium alloys include lithium-aluminum, lithium-lead, lithium-magnesium, lithium-bismuth, lithium-gallium, lithium-indium, lithium-gallium-indium, etc., and alloys containing small amounts of other metals. Things are used.

〔Example〕

Next, the present invention will be explained in more detail by giving Examples.

Example 1 0.1 mol/i aniline and 1 mol/f HBF,
Polyaniline was electrolytically polymerized on a platinum electrode using a potential scanning method in an aqueous solution in which polyaniline was dissolved. This polyaniline was scraped off from the platinum electrode, and the obtained polyaniline powder was washed and vacuum dried.
Pressure molded at a molding pressure of 00 kg/cd, diameter 14i+
A pellet with a thickness of 0.85+sm was prepared and used as a positive electrode. For the negative electrode, 7μ metallic lithium was used.

The electrolyte contained 37.5 g of LiBF in an argon atmosphere.
4 was gradually dissolved in 1,2-dimethoxyethane and the total amount was 100mj! LiBF with an ifi degree of 4 mol/l was used.

As shown in FIG. 1, the battery includes, in a plastic experimental cell container 1, a current collector 3 made of a stainless steel foil net with leads 2 made of stainless steel foil, a negative electrode 4 made of the above-mentioned lithium, A separator 5 made of a microporous polypropylene film, and a positive electrode 6 made of the polyaniline pellets mentioned above.
, a current collector 7 made of a stainless steel net with leads 8 made of stainless steel foil are arranged in this order, and the electrolyte 9 is
7μ! After the injection, a plastic stopper 10 was placed on top, and the gap was solidified and sealed with epoxy resin 11 to assemble.

Example 2 A battery was assembled in the same manner as in Example 1, except that the LiBFs concentration of the electrolyte was changed to 5 mol/l and the amount of electrolyte injected was changed to 159 μ2, which is the same capacity as polyaniline.

Example 3 A battery was assembled in the same manner as in Example 1, except that the electrolyte was changed from 1 degree LiBFa to 6 mol/i, and the amount of electrolyte injected was changed to 134 μ2, the same capacity as polyaniline.

Comparative Example 1 A battery similar to Example 1 was assembled except that the LiBFn concentration of the electrolyte was changed to 1 mol/2 and the amount of the electrolyte injected was changed to 756 μl, which was the same volume as polyaniline.

The batteries of Examples 1 to 3 and Comparative Example 1 were charged at a constant current of 500μA until the positive electrode became 3.9μ with respect to the negative electrode.
Constant current discharge was carried out at 500 μA until the positive electrode became 2.5 V with respect to the negative electrode, and after repeating this charging and discharging twice, the discharge capacity at the third discharge was measured. Table 1 shows the energy density per volume and weight of the battery calculated based on the results and the above measurement results of the discharge capacity.

As shown in Table 1, in each battery, a predetermined discharge capacity can be obtained by injecting an amount of electrolyte corresponding to the amount of polyaniline (however, the increase in LIBF4 concentration in the electrolyte Accordingly, the resistance polarization increases and the discharge capacity slightly decreases), Examples 1 to 1 of the present invention
In battery No. 3, the energy density per volume and energy density per weight were significantly improved compared to the battery of Comparative Example 1, which corresponds to the conventional product, by reducing the amount of electrolyte injected as the LIBF4 concentration increased. was completed.

Further, the charge/discharge cycle was repeated under the above conditions, and the 10th
The discharge capacity at the 0th discharge was measured, and the retention rate of the discharge capacity with respect to the discharge capacity at the 3rd discharge was determined. The results are shown in Table 2.

Table 2 As shown in Table 2, LiBF was present in 1,2-dimethoxyethane at 4 mol/115 mol/2.6 mol/j! The batteries of Examples 1 to 3 using the dissolved electrolyte had a high discharge capacity retention rate, and the LiBF concentration in the electrolyte was 1 mol/L.
2, the Li in the electrolyte was the same as that of Comparative Example 1.
No deterioration in charge/discharge cycle characteristics due to increasing the BF concentration was observed.

〔Effect of the invention〕

As explained above, in the present invention, in a lithium secondary battery using polyaniline as a positive electrode, LiBF is used in 1.
By using an electrolytic solution in which 4 mol/l to 6 mol/Il was dissolved in 2-dimethoxyethane, the energy density per volume and weight could be increased.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a lithium secondary battery according to the present invention. 4... Negative electrode, 6... Positive electrode, 9... Electrolyte solution #1 Fig. 4... Negative electrode 6... Positive electrode 9... Electrolyte solution

Claims (1)

[Claims] (1) In a lithium secondary battery that uses polyaniline as the positive electrode and lithium or lithium alloy as the negative electrode, LiBF_4 is used as the solute of the electrolyte, 1,2-dimethoxyethane is used as the solvent of the electrolyte, and the solute of the electrolyte is A lithium secondary battery having a concentration of 4 mol/l to 6 mol/l.