JPS6280977A - Organic electrolyte battery - Google Patents

Abstract

PURPOSE:To increase thermostability by constituting with a positive electrode, a negative electrode comprising lithium or lithium alloy, and electrolyte solution, and using organic electrolyte solution prepared by adding morpholine as a stabilizer to a specified lithium salt of Lewis acid and organic solvent as the electrolyte solution. CONSTITUTION:Morpholine whose fourth positive is substituted with alkyl group having the carbon number of 1-4 is added as a stabilizer to electrolyte using lithium salt of Lewis acid indicated in the formula LiMFe as a solute. The morpholine having alkyl group of the carbon number of 1-4 has ether bond tertiary amine in its molecule shown in the formula and stabilizes electrolyte. The adding amount of 4-alkyl morpholine is preferable to be 0.2-2 times mol of the salt of Lewis acid and the amount of lithium salt of Lewis acid is usually 0.1-3mol/dm<3> in the electrolyte. Thereby, thermostability of electrolyte is increased and deterioration in performance during storage is retarded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to organic electrolyte batteries, and more particularly to improvements in their electrolyte solutions (hereinafter referred to as electrolytes).

[Conventional technology]

Recently, the general formula (
1) % formula % (1) (wherein M is P, As, Sb or B, n is M is P,
Lewis acid lithium salts (6 when As or Sb, 4 when M is B) have large f4 solubility, high conductivity, and are safer than perchlorate-based ones. Therefore, it has come to be widely used (for example, U.S. Patent No. 3,607,020, U.S. Patent No. 3,9
No. 07,977).

However, the Lewis acid lithium salt represented by the above general formula (1) has a problem with stability, especially at high temperatures, and decomposes during storage at high temperatures, causing decomposition and polymerization of the electrolyte solvent. There was a problem in that the battery performance was significantly degraded, such as by increasing internal resistance and decreasing closed-circuit voltage.

(Problems to be Solved by the Invention) This invention solves the problem that the electrolyte of the conventional battery lacks thermal stability, improves the thermal stability of the electrolyte, and prevents the deterioration of battery performance during storage. The purpose is to provide a battery with less organic electrolyte.

[Means for solving problems]

This invention provides an electrolytic solution by adding morpholine substituted at the 4-position with an alkyl group having 1 to 4 carbon atoms as a stabilizer to an electrolytic solution containing a Lewis acid lithium salt represented by the general formula (1) as a solute. This improves the thermal stability of the battery and reduces the deterioration of battery performance during storage.

In the present invention, the morpholine having an alkyl group having 1 to 4 carbon atoms at the 4-position (hereinafter referred to as 4-alkylmorpholine), which is added as a stabilizer to the electrolytic solution in order to improve the thermal stability of the electrolytic solution, is as follows. As shown in the structural formula, it has an ether bond and a tertiary amine in the molecule (in the formula, R is an alkyl group having 1 to 4 carbon atoms). It coordinates to form a complex, suppresses the reaction between Li+ ions and F- ions generated by decomposition of PF5- ions, and stabilizes the electrolyte. In addition, HF (
It has a basicity that neutralizes the acidity of hydrogen fluoride).
Shows stabilizing effect even in small amounts.

The larger the amount of 4-alkylmorpholine, the greater the effect of stabilizing the electrolyte, and from this point of view, it is preferable to add a large amount, but if it is too large, the conductivity at low temperatures and the charging performance of a secondary battery may be affected. Since the discharge characteristics are deteriorated, the amount added is preferably 0.2 to 2 times the mole of the Lewis acid salt represented by the general formula.

In the present invention, the general formula (I
), M is P(
LtPFs (lithium hexafluorophosphate), which is
Li5bFs (lithium hexafluoroantimonate) where M is Sb (antimony), LiAsF5 (lithium hexafluoroarsenate) where M is As (arsenic), M is B
(boron), LiBF4 (lithium tetrafluoroborate).

The electrolytic solution is a Lewis acid lithium salt represented by the general formula (1), for example, propylene carbonate, T-
Butyrolactone, tetrahydrofuran, 1.2-dimethoxyethane, 112-jethoxyethane, 1.3-dioxolane, 4-methyl-1,3-dioxolane, etc. alone or dissolved in a mixed solvent of 2 ft or more, and the above-mentioned 4- Adding the alkylmorpholine or adding the 4-alkylmorpholine to the organic solvent and then
It is cleaved by dissolving the Lewis acid lithium salt represented by the general formula (1). In short, in the present invention, it is sufficient that the electrolytic solution contains the above-mentioned 4-alkylmorpholine, and the above-mentioned 4-alkylmorpholine and the general formula (1
) The order of addition with the Lewis acid lithium salt shown in ) does not matter. In addition, the electrolytic solution to which 4-alkylmorpholine is added as a stabilizer has good thermal stability and excellent storage characteristics as described above, as well as being difficult to charge when used as a secondary battery. It also has the feature of excellent discharge characteristics.

The amount of the Lewis acid lithium salt represented by the general formula (1) in the electrolytic solution is usually 0.1 to 3 mol/dm3.

In the battery of the present invention, lithium or a lithium alloy is used for the negative electrode. Examples of lithium alloys include lithium-aluminum, lithium-lead, lithium-gallium, lithium-indium, and lithium-gallium.
Lithium alloys such as indium, lithium-magnesium, and lithium-zinc are used. Examples of active materials for the positive electrode include titanium disulfide (TiS2), molybdenum disulfide (MoS2), and molybdenum trisulfide (MoS2).
2S), zirconium sulfide (ZrS2), niobium disulfide (NbS2), phosphorous nickel trisulfide (NiPS3), vanadium selenide (VSe2), iron sulfide, copper oxide, carbon fluoride, etc. are used. Particularly in the production of secondary batteries, titanium disulfide is preferably used because it has a layered crystal structure and has a large diffusion constant for lithium.

〔Example〕

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

Example 1 LiPF6 was added to a mixed solvent of 58% by volume of 4-methyl-1,3-dioxolane, 38.7% by volume of 1,2-dimethoxyethane and 3.3% by volume of 4-methylmorpholine as an electrolytic solution. Using an organic electrolyte solution dissolved to give dm3, a lithium-aluminum alloy containing 40 atomic percent lithium for the negative electrode, and a molding mixture containing titanium disulfide as the positive electrode active material for the positive electrode, a molding mixture as shown in Figure 1 was prepared. A lithium organic electrolyte battery was assembled. In the above electrolyte, the amount of 4-methylmorpholine is approximately 0.0% of LiPF5.
This corresponds to 3 times the mole.

In Fig. 1, 1 is a negative electrode can, which is made of stainless steel and has a nickel plated surface, and 2 is a negative electrode side current collection network made of stainless steel, which is spotted on the inner surface of the negative electrode can 1. Welded. 3 is a negative electrode made of the aforementioned lithium-aluminum alloy, and 4 is a separator made of microporous polypropylene film. 5 is an electrolyte absorber made of polypropylene non-woven fabric, 6 is a positive electrode formed by pressure molding a mixture containing titanium disulfide as the positive electrode active material into a pellet shape, and 7 is a positive electrode side current collector mesh made of stainless steel. be. 8 is a positive electrode can made of stainless steel and whose surface is plated with nickel, and 9 is an annular gasket made of polypropylene. The theoretical amount of electricity at the negative electrode of this battery is approximately 30 m
Ah, and the theoretical amount of electricity of the positive electrode is 13 mAh.

Example 2 4-methyl-1,3-dioxolane 57.
Except for using an organic electrolyte solution in which LiPF5 was dissolved in a mixed solvent consisting of 8% by volume, 38.5% by volume of 1.2-dimethoxyethane, and 3.7% by volume of 4-ethylmorpholine so that A lithium organic electrolyte battery similar to that in Example 1 was assembled. In the above electrolytic solution, the amount of 4-ethylmorpholine is about 0.3 times the mole of LiPF6.

Comparative Example An organic electrolyte solution in which LiPF6 was dissolved in L mol/dm' in a mixed solvent consisting of 60% by volume of 4-methyl-1,3-dioxolane and 40% by volume of 1,2-dimethoxyethane was used as the electrolyte solution. A lithium organic electrolyte battery was assembled in the same manner as in Example 1 except for the following.

The batteries of Examples 1 and 2 and the batteries of Comparative Example were stored at 60°C, and the internal resistance change due to storage was 10 kHz and 30 kHz.
Changes in closed circuit voltage after 5 seconds of discharge at 0Ω were investigated. 10kH
z Changes in internal resistance are shown in Figure 2, and changes in closed circuit voltage are shown in Figure 3. Note that the internal resistance at 10 kHz is a resistance that substantially depends on the electrolyte.

As shown in FIG. 2, in the battery of Comparative Example, which is a conventional battery, a significant increase in internal resistance occurred as the number of days of storage increased, but in the batteries of Examples 1 and 2 of the present invention, such a large increase occurred. No increase in internal resistance was observed.

Furthermore, as shown in FIG. 3, the batteries of Examples 1 and 2 of the present invention exhibited less decrease in closed circuit voltage during storage and had excellent storage characteristics than the batteries of Comparative Examples.

Next, the results of investigating the charging and discharging characteristics of the electrolytes used in the batteries of Examples 1 and 2 and the batteries of Comparative Example are shown in the fourth section.
As shown in the figure. The test was conducted using an aluminum electrode as a working electrode, lithium as a counter electrode, lithium as a reference electrode, and the electrolyte used in the batteries of Examples 1 and 2 and the comparative example. This was done by assembling a model cell and depositing lithium on an aluminum electrode to measure the charge/discharge characteristics of the lithium electrode. First, the measurement was carried out at a constant current of 0.5 mA/cA for 20
Time (10mAh) Lithium was electrodeposited on the aluminum electrode and discharged at a constant current of 0.2A/cd until the potential was 3V.
Find the relationship between the capacity and the number of cycles until the 4th
The figure shows the relationship between the charge/discharge efficiency and the number of cycles.

As shown in FIG. 4, the charging and discharging characteristics of the electrolytes used in the batteries of Examples 1 and 2 were excellent.

In addition, although the example shows the case where LiPF6 is used as the Lewis acid lithium salt represented by the general formula (1), it goes without saying that the present invention is also applicable to cases where LiAsF6, LiSbF6, LiBF4, etc. are used. Nor.

〔Effect of the invention〕

As explained above, in the present invention, by adding 4-alkylmorpholine as a stabilizer, the thermal stability of the electrolytic solution can be increased and a decrease in battery performance during storage can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of an organic electrolyte battery according to the present invention. FIG. 2 is a diagram showing the 10kHz internal resistance change during storage of the batteries of Examples 1 and 2 of the present invention and the comparative example, and FIG. FIG. 3 is a diagram showing a change in closed circuit voltage as the battery is stored. Fourth
The figure is a diagram showing the relationship between the number of cycles and the charge/discharge efficiency of model cells assembled using the electrolytes used in the batteries of Examples 1 and 2 of the present invention and the batteries of Comparative Example. 3...Negative electrode, 6...Positive electrode 1 Figure 3...Negative electrode Figure 2 Storage period (days) Figure 3 Storage period (days) Figure 4 Number of cycles

Claims (3)

[Claims] (1) A positive electrode, a negative electrode made of lithium or a lithium alloy, and an electrolyte solution, and the electrolyte solution has a solute of the general formula (I) LiMFn(I) (where M is P, As, Sb, or B). , n is M is P,
A Lewis acid lithium salt represented by 6 when As or Sb and 4 when M is B), the solvent is an organic solvent, and the stabilizer has an alkyl group having 1 to 4 carbon atoms at the 4-position. An organic electrolyte battery characterized by being an organic electrolyte solution containing morpholine. (2) The organic electrolyte battery according to claim 1, wherein the alkyl group at the 4-position of the morpholine is a methyl group or an ethyl group. (3) The organic electrolyte battery according to claim 1 or 2, wherein the positive electrode active material is titanium disulfide and the Lewis acid lithium salt represented by the general formula (I) is LiPF_6.