JPS6386357A - Nonaqueous electrolyte battery - Google Patents

Abstract

PURPOSE:To make the production of a battery easy and to retard the generation of decomposition product to increase the performance by using a nonaqueous electrolyte in which sodium ions in organic solvent are replaced with lithium ions. CONSTITUTION:An organic electrolyte is prepared by dissolving sodium hexafluorophosphate in a mixture of dioxolane and dimethoxyethane which are purified by distillation. The organic electrolyte is put into a container, and electrolysis is conducted by using a lithium plate on an anode and a nickel plate as a cathode. With the progress of the electrolysis, lithium ions dissolve in the electrolyte from the lithium plate and sodium having reduction potential different from lithium preferentially deposits on the nickel plate, and finally sodium ions in the electrolyte are replaced with lithium ions. A positive elec trode 1 is pressed against the inner bottom of a positive can 3 through a current collector 2, and the obtained electrolyte is poured on the positive electrode 1, then a battery is assembled.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides lithium hexafluorophosphate LiPF6
The present invention relates to a non-aqueous electrolyte battery constructed using a non-aqueous electrolyte containing substantially as a solute.

<Conventional technology> Non-aqueous electrolyte batteries use a negative electrode whose active material is an alkali metal or alkaline earth metal such as lithium or sodium, and a positive electrode mixture whose active material is manganese dioxide or carbon fluoride. The electrolyte is a nonaqueous organic solvent such as propylene carbonate, γ-butyrolactone, dimethoxyethane, or tetrahydrofuran, and an alkali metal salt such as lithium perchlorate, lithium tetrafluoroborate, or lithium hexafluorophosphate. The structure uses a non-aqueous electrolyte that is mixed and dissolved as a solute.

Among the solutes used in the above non-aqueous electrolyte, lithium hexafluorophosphate L! PF6 has high ionic conductivity, so an electrolyte using it can improve battery performance, and compared to LICJ204 lithium perchlorate, it has the advantage of being highly safe with no risk of explosion, etc. It is known as a solute in electrolytes for non-aqueous electrolyte secondary batteries.

<Problems to be Solved by the Invention> However, the above-mentioned lithium hexafluorophosphate is extremely unstable in the crystalline state, and gradually decomposes even at room temperature as shown in the following formula (■), and water is present even in vIin. Then, there is a drawback that it is hydrolyzed as shown in formulas ① and 0.

(When water does not exist) ■LiPF6→L i F1PF5 (When water exists) ■LiPFG Tomachi O → Li F+POF3+2HF ■POF3 +3H20-)H3PO4+3HF Note that lithium hexafluorophosphate LtPF6 is a non-aqueous solvent solution Stable when dissolved in
up to about 80°C).

Therefore, when storing it, or when mixing it with a solvent and dissolving it, it is necessary to store it under an inert atmosphere, and to work while suppressing the temperature rise due to the heat of dissolution during mixing. Therefore, strict management is required for its storage and handling. Furthermore, even with such management, it is practically difficult to completely suppress the above-mentioned decomposition, and there is a problem in that the decomposition products cause polymerization of the solvent in the electrolytic solution, resulting in a decrease in battery performance.

<Means for Solving the Problems> The non-aqueous electrolyte battery of the present invention is produced by dissolving sodium hexafluorophosphate in a non-aqueous solvent and replacing the sodium ions in this organic solvent with lithium ions. The gist is that a non-aqueous electrolyte was used.

As a specific means for the above-mentioned substitution treatment, the above-mentioned organic solvent in which sodium hexafluorophosphate is dissolved,
One example is a method of electrolysis using lithium as an anode.

<Function> By using the above means, a non-aqueous electrolyte having substantially the same composition as that obtained by dissolving lithium hexafluorophosphate in an organic solvent in a crystalline state can be obtained. In this case, the crystals of sodium hexafluorophosphate are stable at room temperature and do not undergo hydrolysis, so the above-mentioned decomposition will not occur as in the case of using crystals of lithium hexafluorophosphate, making it easier to manufacture and handle. This makes it extremely easy to use the decomposition products, and also suppresses deterioration in battery performance caused by the decomposition products.

<Example> A solvent of 20 mN (
Moisture value 30mM! 2)1. : An organic electrolyte was prepared by dissolving 62.35 g (0.7 molar concentration) of sodium hexafluorophosphate NaPF. This organic electrolyte was placed as an electrolyte in a Teflon container, and the size was 25 mm x 15 m.
Using a lithium plate with a size of m as an anode and a nickel plate with the same size as a cathode, electrolysis was carried out for 19 hours at a current of 3QmA (current density 8mA/c1). As electrolysis progresses, lithium ions L1 are eluted from the lithium plate into the electrolyte, while true sodium, which has a reduction potential compared to lithium, is preferentially deposited on the nickel plate, and in the end, sodium ions L1 elute from the lithium plate into the electrolyte. A reaction occurred in which Na was replaced by lithium ions L1.

In addition, since a considerable amount of lithium eutectoids on the nickel plate at the final stage of electrolysis, in order to sufficiently perform the above substitution,
It is necessary to conduct the above electrolysis by applying a larger amount of electricity than the theoretical value. In this example, an amount of electricity of 150% of the theoretical value was applied.

Then, a positive electrode 1 made of a mixture of titanium disulfide TiS2, graphite, and PTFE powder in a weight ratio of 4:1:0.4 and pressure-molded into a disk shape was passed through a positive electrode current collector 2 made of stainless steel net. 5US304 to the inner bottom surface of the positive electrode can 3, and the electrolytic solution subjected to the above substitution treatment was applied to the positive electrode 1 for 12 hours.
By injecting the liquid at 0μ℃ and absorbing it, the diameter 2 as shown in Fig.
A battery of the present invention having a diameter of 0 mm and a height of 1.6 mm was assembled. In the figure, 4 is a separator made of propylene nonwoven fabric, 5 is a lithium negative electrode, 6 is a negative electrode terminal made of SUS 304, and 7 is a sealing gasket made of polypropylene.

On the other hand, 2.13 g of commercially available lithium hexafluorophosphate (0.7 molar temperature:
A conventional battery was prepared under the same conditions as the above-described battery of the present invention except that a non-aqueous electrolyte was prepared by dissolving a non-aqueous electrolyte (sealed and stored in a Teflon container in an argon atmosphere).

Ten cells of each of the batteries of the present invention and the conventional battery were stored at an ambient temperature of 60'C, and the changes over time in the internal resistance (RAo) (average value of each of the ten cells) were investigated. The results are shown in Figure 2. The internal resistance of the battery of the present invention increased by only about 40% even after 30 days of storage, while the internal resistance of the conventional battery increased by about 5 times compared to the initial value after 30 days. Indicated.

The reason for this remarkable increase in internal resistance in conventional batteries is that some of the crystals of lithium hexafluorophosphate used as a solute in the non-aqueous electrolyte decompose during storage or when dissolved in a solvent. Due to the action of this decomposition product, part of the solvent polymerized during storage, increasing the viscosity of the electrolyte, and at the same time, this decomposition product reacted with the lithium of the negative electrode to form an insoluble film on the surface of the lithium negative electrode. This seems to be the main cause. In the battery of the present invention, the degree of increase in the viscosity of the electrolytic solution and the formation of a film are small, so the degree of increase in internal resistance is small, and it is considered that the battery has excellent storage characteristics.

It goes without saying that the present invention can be applied to primary and secondary non-aqueous electrolyte batteries.

<Effects of the Invention> According to the non-aqueous electrolyte battery of the present invention configured as described above, the ease of handling when producing a non-aqueous electrolyte that essentially uses lithium hexafluorophosphate Li PF6 as a solute is improved. In addition, the production of the battery is facilitated, and the production of the decomposition products is significantly suppressed, resulting in improved battery performance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the battery of the example, and FIG. 2 is a graph showing the storage characteristics of the battery of the present invention and the conventional battery. 1... Positive electrode, 4... Separator, 5... Lithium negative electrode.

Claims (1)

[Claims] 1. A non-aqueous electrolyte is used, which is obtained by dissolving sodium hexafluorophosphate in a non-aqueous organic solvent and replacing the sodium ions in the organic solvent with lithium ions. non-aqueous electrolyte battery. 2. The non-aqueous electrolyte battery according to claim 1, wherein the replacement treatment is performed by electrolysis using lithium as an anode.