JPH0837025A - Nonaqueous electrolyte - Google Patents

Abstract

PURPOSE:To provide a non-aqueous electrolyte which is for a battery using alkali metal or carbonic material in its negative electrode and is unlikely to decompose on electrode at the time of charging and discharging by preparing the electrolyte using a solvent of trifluoropropylene carbonate as expressed by the formula given beside. CONSTITUTION:A non-aqueous electrolyte is prepared by using as a part or the whole a solvent of trifluoropropylene carbonate TFPC as expressed by Formula I given beside. The TFPC may be used either solely or as a mixture with any other solvent, and in thelatter case, it is preferable to contain 50% or more TFPC. The synthetization of TFPC is conducted by putting a dried lithium bromide in a flask, substituting with carbon dioxide gas, adding N- methyl pyrolidone, and dissolving. Trifluoropropylene oxido is added to the obtained solution, and the resultant is agitated in a carbon dioxide gas atmosphere. Ether is added to a liquid containing products, followed by rinsing with water, addition of sodium sulfate anhydride, and drying, and then the obtained residue is distilled decompressively, and TFRC is collected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic solution for a battery using an alkali metal or carbon material as a negative electrode.

[0002]

2. Description of the Related Art Batteries using an alkali metal or carbon material as a negative electrode are expected to be researched because they can increase cell voltage and energy density as compared with conventional alkaline batteries and NiCd batteries. . As a typical example, a carbon material capable of intercalating lithium in the negative electrode, a composite material containing lithium cobalt oxide in the positive electrode,
A lithium secondary battery made of a non-aqueous electrolyte is known.

Due to the strong reducing power of lithium, a lithium secondary battery can be manufactured with an electromotive force of about 4V. However, since problems such as irreversible progress of reaction on the positive electrode or the negative electrode, alteration of the positive electrode active material, and dimensional change have not been solved, a high electromotive force lithium secondary battery has a theoretical voltage of about 4 V Actually due to decomposition of the liquid, etc. 3.
In the present situation, only a voltage of about 6 to 3.8 V has been put into practical use.

One of the problems with these lithium secondary batteries is the decomposition of the solvent on the electrodes. Non-aqueous electrolyte is LiC
lO _4, LiPF _6, solvent and ethylene carbonate, such as LiAsF ₆ (EC), propylene carbonate (P
A solution using C), DEC (diethyl carbonate), 2-methyl-tetrahydrofuran or the like as a solvent is general. However, at a voltage of about 4 V, these solvents decompose on the electrodes during charging and discharging and hinder the battery reaction. As a result,
The charge / discharge capacity and efficiency were extremely poor. In order to suppress the decomposition of the solvent, a mixture of two or more kinds of solvents and halogenation of solvent molecules (Japanese Patent Laid-Open Nos. 62-290071 and 62-21756)
Although measures such as 7) have been taken, they have not always been effective.

[0005]

Under these circumstances, the present invention provides an electrolytic solution for use in a battery having an alkali metal or carbon material as a negative electrode, which is not easily decomposed on the electrode during charging and discharging. The purpose is to provide a water electrolyte.

[0006]

Means for Solving the Problems The present inventor has paid attention to halogenation of a solvent, and as a result of earnestly examining the halogenation of propylene carbonate, the present inventors have used trifluoropropylene carbonate as at least a part thereof as a solvent of an electrolytic solution. By doing so, it was found that the potential stability of the solvent was improved as compared with the case of using propylene carbonate, and the present invention was accomplished.

That is, the present invention is a nonaqueous electrolytic solution for a battery having an alkali metal or carbon material as a negative electrode, in which trifluoropropylene carbonate represented by the following formula is used as a part or all of the solvent. .

[0008]

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The above-mentioned trifluoropropylene carbonate used in the present invention is a novel substance (this substance is separately applied as Japanese Patent Application No. 5-310343). This can be prepared, for example, as follows.

That is, trifluoropropylene oxide represented by the following formula

[0011]

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Can be prepared by reacting with carbon dioxide.

Trifluoropropylene carbonate (hereinafter abbreviated as TFPC) may be used alone or in a mixture with other solvent. When used by mixing with another solvent, TFPC is contained in an amount of 30% or more, preferably 50% or more. Examples of the other solvent that can be used in the electrolytic solution of the present invention include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, dimethoxyethane, 2-methyltetrahydrofuran, and THF.

As the solute used in the electrolytic solution of the present invention,
Li salts such as LiClO ₄ , LiPF ₆ and LiAsF ₆ are preferred. The solute concentration is preferably 0.5 to 1.5 M / l. If it is less than 0.5 M / l, sufficient conductivity cannot be obtained,
If it exceeds 1.5 M / l, lithium salt is precipitated.

The non-aqueous electrolyte of the present invention is used for a primary battery or a secondary battery having an anode of an alkali metal such as Li or a Li alloy or various carbon materials as a negative electrode, but other constituent elements of the battery are not particularly limited. .

[0016]

Embodiments of the present invention will be described below.

Example Synthesis of TFPC 0.65 g (7.5 m) of dried lithium bromide (anhydride)
(mol) was placed in a round-bottomed flask and replaced with carbon dioxide gas, and 12.5 ml of dried N-methylpyrrolidone was added and dissolved. 4.3 ml (50 mmol) of trifluoropropylene oxide was added to the obtained solution, and the mixture was stirred at room temperature (about 25 ° C) for 24 hours under a carbon dioxide gas atmosphere. Then, 80 ml of ether was added to dilute the liquid containing the reaction product, and the mixture was washed 8 times with 20 ml of water. After adding anhydrous sodium sulfate and drying, the ether in the solution was distilled off, and the resulting residue was distilled under reduced pressure to obtain 100 ° C to 105 ° C / 29 ° C.
A fraction of mmHg was collected. This fraction is proton NMR
( ¹ H-NMR), infrared absorption spectrum (IR), ¹³ C
-NMR, ¹⁹ F-NMR and gas chromatography-mass spectrometry revealed that it was the target trifluoropropylene carbonate (TFPC). The fraction recovered as a purified product was 3.85 g, and the yield based on the starting material trifluoropropylene oxide was 49%.

Using the TFPC thus obtained, 1M
A LiClO ₄ -TFPC solution was prepared and the conductivity, discharge capacity and discharge efficiency of this solution were measured. The conductivity is lithium (circular shape, diameter 7.5 mm, thickness 1.0 mm), and 1 M LiClO ₄ -TFPC impregnated in a glass filter.
(Circular type, diameter 7.5 mm, thickness 1.0 mm, TFPC =
25 mg) and a half battery having a structure sandwiched between
C impedance measurement (5 to 10 ⁵ Hz) to Cole
-Cole plot was used. The discharge capacity is Teflon (trademark) and carbon powder (mixing ratio: carbon 97 wt
%) Compression molded pellets (circular shape, diameter 7.5 mm,
A thickness of 0.3 mm is used as a test electrode, lithium (circular shape, diameter 7.
5 mm, thickness 1.0 mm) as a counter electrode, and a battery having a structure in which 1 M LiClO ₄ -TFPC impregnated in a glass filter was sandwiched between the test electrode and the counter electrode was prepared, and a current of 0.5 mA / cm ² was charged / discharged. The capacity at the time of charging when charging and discharging were performed under the condition of voltage 0 to 1.5V. The discharge efficiency was a value obtained by dividing the charge capacity by the discharge amount. In a battery having lithium as a counter electrode and a pellet obtained by compression molding Teflon and carbon powder as a test electrode, lithium ion intercalation into carbon during discharge corresponds to deintercalation during charging.

Comparative Example 1 Measurement was carried out in the same manner as in Example except that the test solution was 1M LiClO ₄ -propylene carbonate.

Comparative Example 2 Measurement was carried out in the same manner as in Example except that the test solution was 1M LiClO ₄ -ethylene carbonate.

[0021]

[Table 1]

Example 2 91% by weight of lithium cobalt oxide, 6% by weight of carbon powder,
And 3% by weight of Teflon (trade name) were kneaded to give a thickness of 100
After being formed into a sheet of μm, it was punched out into a circle having a diameter of 7.5 mm, which was used as a positive electrode. Further, the diameter is 7.5 mm and the thickness is 0.
3M glass filter with 1M LiClO ₄ TFPC
The solution was impregnated and used as the electrolyte. Then, a battery was prepared by using metallic lithium having a diameter of 7.5 mm and a thickness of 1 mm as the negative electrode. The battery was subjected to a charge / discharge test under the following conditions. The result is shown in FIG.

Charge / Discharge Conditions Charge side: Current density 1 mA / cm ² cut-off voltage 4.2 V Discharge side: Current density 1 mA / cm ² cut-off voltage 3.0 V Comparative Example 3 1 M LiClO ₄ PC solution was used as the electrolyte, and the others were used. A battery was prepared and a charge / discharge test was conducted in the same manner as in Example 2. The result is shown in FIG.

As is apparent from FIG. 1, when the nonaqueous electrolytic solution of the present invention is used, it can be used stably for a long period of time.

Example 3 As electrolytes, 1M LiClO ₄ TFPC: EC (volume ratio 1: 1), 1M LiClO ₄ TFPC: PC (volume ratio 1: 1) and 1M LiClO ₄ TFPC: DEC.
Using (Volume ratio 1: 1), a battery was prepared in the same manner as in Example 2 except for the above, and a charge / discharge test was conducted.

The results are shown in Table 2.

[0027]

[Table 2]

[0028]

As described above, the battery using the trifluoropropylene carbonate of the present invention as the non-aqueous electrolyte can improve the battery performance as compared with the case of using ethylene carbonate or propylene carbonate.

[Brief description of drawings]

FIG. 1 is a graph showing charge / discharge test results.

Claims (1)

[Claims] 1. A non-aqueous electrolytic solution for a battery using an alkali metal or carbon material as a negative electrode, wherein trifluoropropylene carbonate represented by the following formula is used as a part or all of a solvent. Embedded image