JPH01134873A - Organic electrolyte secondary battery - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to the improvement of organic electrolyte secondary batteries using lithium or the like as a negative electrode. The aim is to improve discharge characteristics.

Conventional technology Lithium or lithium alloy is used as the negative electrode, and titanium disulfide (TiS2), manganese dioxide (MnO), and aluminum sesquioxide (Cr20s) are used as the positive electrode as active materials.
Research is actively being conducted on organic electrolyte secondary batteries using electrodes made by mixing carbon powder such as acetylene black as a conductive agent. The electrolytes in these batteries include propylene carbonate (PC) and ethylene carbonate).
Dimethoxyethane (
DME), 2-methyltetrahydrofuran (2-Me
Organic electrolytes have been used in which lithium perchlorate (LiCl 04 ) or lithium hexachloroarsine (LiAsF6) is dissolved as a solute in a mixed solvent containing ethers such as -T HF ).

Problems to be solved by the invention Conventional PC has a high dielectric constant but a high viscosity.
When used in batteries, a drop in voltage and a drop in the utilization rate of the positive electrode occur during high rate discharge. On the other hand, ethers such as DME and 2-Me-THF have low viscosity but low dielectric constant, so
It was not possible to ionically dissociate the solute L LCl at a sufficient rate, resulting in a decrease in battery voltage and a decrease in utilization rate during high rate discharge. For this reason, carbonates such as PC+EC and ethers have been mixed to obtain sufficient ionic dissociation of the solute and to reduce the viscosity, thereby improving the discharge characteristics of the battery. However, when a battery is over-discharged in these electrolytes, the potential of the positive electrode decreases, causing PC to form on the surface of the active material and the surface of the carbon powder used as the conductive agent.
The decomposition of carbonate solvents such as EC and EC occurred, and the decomposition products covered the surfaces of the positive electrode particles, resulting in a sharp decline in charge/discharge characteristics thereafter.

In view of the problems of the prior art described above, the present invention, in place of PC and EC, has the ability to sufficiently dissociate solutes such as LiC1, and does not decompose even if the potential of the positive electrode decreases due to overdischarge. The purpose of the present invention is to provide a battery that uses a solvent.

Means for Solving the Problems The present invention provides the following advantages:1.
The secondary battery is characterized in that it uses a mixed solvent containing 3-dioxolane-2,5 dione.

Effect: By using a mixed solvent of ethers and 1,3-dioxolane-2,5-dione, it seems that sufficient ionic dissociation of the solute occurs. Charge/discharge characteristics equivalent to or better than those obtained during over-discharge can be obtained, and even if over-discharge is performed, there is little decomposition of the solvent, unlike when using PC or EC, and sufficient charge-discharge can be performed thereafter.

Example The present invention will be explained in detail below.

(Example 1) A lithium disk having a diameter of 17.5 ml and a thickness of 0.5 ml was used as a negative electrode. The theoretical filling amount at this time is 247 m
Ah. For the positive electrode, 0.4 g of a mixture of 100% manganese dioxide, 10 parts by weight of acetylene black as a conductive agent, and 10 parts by weight of polytetrafluoroethylene resin as a binder was mixed into a disk shape with a diameter of 17.5 ff. The material was compression molded. The theoretical filling capacity of this positive electrode is 103 m
It was Ah. A flat battery shown in FIG. 1 was constructed using these positive and negative electrodes, and differences in characteristics due to differences in organic electrolytes were investigated.

In FIG. 1, 1 is a battery case, 2 is a sealing plate, 3 is a negative electrode, 4 is a separator, 6 is a positive electrode, and 6 is a gasket.

As the solute in the organic electrolyte, Li (
JO4 was used. A battery using a mixed solvent of 1.3-dioxolane-2,5-dione and DME at a molar ratio of 6:10 as the mixed solvent of the organic electrolyte was used as the solvent of the present invention. .3-dioxolane-2,5-
A battery using dione and 2-Me-THF is designated as B. In addition, as a conventional example, a battery using 6:10 PC and DME is the same as C1 (a battery using 5:10 PC and 2-Me-T HF is D, and a battery using 2-Me-T HF alone is the same as C1). Let the battery be E.

Each battery was discharged at 2 mA to 2 V and charged to 3.9 V for 10 cycles, and from the 11th cycle onward, discharge was performed until the battery terminal voltage reached Ov. Second
The figure shows the discharge curve of each battery at the 16th cycle. This shows that even when overdischarging is performed, good charge-discharge cycles are possible when the mixed solvent of 1,3-dioxolane-2,5-dione of the present invention is used.

Further, FIG. 3 shows the discharge curve of the battery at the 8th cycle before over-discharging. Compared to E, 2-Me-THF alone, B added 1,3-dioxolane-2,5-dione.
It can be seen that the battery exhibited performance equivalent to or better than that of a conventional mixed solvent using PC.

The chemical structure of 1,3-dioxolane-2,5-dione is shown below.

(Example 2) A battery with the same configuration as in Example 1 was prepared, and 1
, 3-dioxolane-2,5 dione and DME were used, and the charge/discharge characteristics were examined by changing the mixing ratio. As the solute, lithium hexafluorophosphine (LiPF6) with a concentration of 1 mol/l was used. The charging and discharging conditions were the same as in Example 1. Figure 4 shows 1,
The discharge capacity at the 15th cycle when overdischarge was created when the molar ratio of 3-dioxolane-2,5-dione was changed was plotted. When N is added to 1 mole of DME and 1,3-dioxolane-2,5-dione is less than 1 mole, L i P
A decrease in discharge capacity, which seems to be due to insufficient ion dissociation of F6, was observed, and when the amount exceeded 30 mol, the viscosity increased,
A decrease in discharge capacity occurred. Therefore, the ratio of 1,3-dioxolane-2,5-dione to DME is 1:1 to 3.
0:10 is good.

(Example 3) The effect of adding 1,3-dioxolane-2,5-dione was investigated in the presence of PC and EC, which separate when overdischarged. Using the same battery as in Example 1, 1,3-dioxolane-2,5-sion:PC:D was used as the mixed solvent of the organic electrolyte.
A battery using an electrolyte with an ME of s: 6:10 is F,
As a conventional example, a battery using an electrolyte with PC:DME of 5=10 is designated as G. Charging and discharging were performed under the same conditions as in Example 1.

FIG. 6 shows the discharge curve of the 16th cycle in which overdischarge was performed. It can be seen that the overdischarge characteristics are improved even when 1,3-dioxolane-2,5-dione is further added to the conventional mixed solvent of PC and DME.

Although the above examples show the case where MnO2 is used as the positive electrode active material, similar effects can be seen when using Tl52, Cr20s, or chromium trioxide (CRSOS). Ta.

Effects of the Invention As described above, according to the present invention, a battery with excellent overdischarge characteristics can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of an organic electrolyte secondary battery according to an embodiment of the present invention, Fig. 2 is a discharge characteristic diagram during charging and discharging after overdischarging the battery using various solvents, and Fig. 3 The figure shows the discharge characteristics during charging and discharging before overdischarging, and Figure 4 shows the discharge characteristics of 1,3
-Characteristic diagram of the discharge capacity of the battery when the molar ratio of dioxolane-2,5-dione is changed. Figure 6 is a diagram of the discharge characteristic diagram during charging and discharging after overdischarging the battery using various solvents. be. A, B, F... Example batteries of the present invention, C, D. E, G... Conventional battery. Name of agent: Patent attorney Toshio Nakao and 1 other person3-
Negative electrode 4-Separator 5-Engineer 1yJ 2nd figure

Claims (2)

[Claims] (1) Consisting of a negative electrode, a positive electrode, and an organic electrolyte, the solvent for the organic electrolyte contains at least 1,3-dioxolane-2,
An organic electrolyte secondary battery characterized by using a mixed solvent containing 5-dione. (2) The molar ratio of 1,3-dioxolane-2,5-dione and other solvents is 1:10 to 30:1.
1. The organic electrolyte secondary battery according to claim 1, wherein the organic electrolyte secondary battery is 0.