JPH0355770A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To improve the charge/discharge characteristics and the discharge characteristics at low temperatures by mixing mixed liquid of specified carbonates with specified solvents to be an organic solvent of electrolyte. CONSTITUTION:For organic solvent of electrolyte consisting of organic solvent including dissolved lithium salt for composing a lithium secondary battery together with electrodes including lithium for active material, mixture of mixed solvents of ethylene carbonate and diethyl carbonate with more than one solvents of 2-methyl tetrahydrofuran, 1,2-dimethox ethane, and 4-methyl, 1,3- dioxolan. A lithium secondary battery having improved charge/discharge characteristics and discharge characteristics at low temperatures can thus be obtained.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a lithium secondary battery.

Conventional technology and its problems Conventionally, lithium secondary batteries use molybdenum disulfide (MoS2) and molybdenum dioxide (Mo05) as positive electrode active materials.
, manganese dioxide (Mn02), vanadium pentoxide (V20,), and other inorganic materials, metallic lithium and lithium ion intercalation and release alloys as negative electrodes, and lithium perchlorate, lithium borofluoride, and hexafluoride as electrolytes. Mixed solutions of lithium salts such as lithium arsenate, dissolved propylene carbonate, and v-methoxyethane are known.

There are many possible configurations depending on the combination of these positive and negative electrodes and electrolytes, but the battery's secondary/I/a
Considering f-density, it is thought that the most advantageous system is a system using gold as the negative electrode. When the battery used as a battery was charged and discharged, a problem occurred in that the battery capacity decreased early due to a decrease in charging and discharging efficiency, which was thought to be caused by lithium dendrites.

As an alternative to this electrolyte, we investigated a mixed solution of ethylene carbonate and 2-methymu-tetophhydronphen using an electrolyte, and found that it improved charge/discharge efficiency by 14%, but it was difficult to use at low temperatures. In this case, a new problem arose: ethylene carbonate solidified.

OBJECTS OF THE INVENTION In view of the above problems, an object of the present invention is to provide a lithium secondary battery with improved charge/discharge characteristics and discharge characteristics at low temperatures.

Structure of the Invention The present invention achieves the above objects, wherein the organic solvent in which the lithium salt is dissolved is a mixed solvent of ethylene carbonate (hereinafter referred to as !CO) and diethyl carbonate (hereinafter referred to as DEO). 2-methyltetophhydrofone (hereinafter referred to as 2Me-THF), 1,2-vmethoxyV ethane (hereinafter referred to as DIE), and 4-methy-1.
At least one WIIJ selected from the group consisting of 5-dioxolane (hereinafter referred to as 4M8-DOL)
Table 1 shows the characteristics of various zero-action solvents for a lithium secondary battery characterized by using a mixed solvent containing &.

EO in Table 1 has a higher dielectric constant than other organic solvents and a high degree of ion dissociation in one electrolytic solution, so it is considered that the conductivity of the electrolytic solution is also high. However, since EO is solid at room temperature, it cannot be used alone.
It was confirmed that the liquid state of 41 was maintained at room temperature by mixing it, and when it was investigated as a solvent for electrolyte solution, it was found that the charge/discharge cycle μ characteristics were good.

Furthermore, a mixed WI medium 6 of go and DIHO, for example 2Me
- It was found that when THF was added to form a mixture of 6 types, the conductivity at low temperatures and the charging/discharging efficiency of the electrolyte were greatly improved. FIG. 1 shows a cross-sectional view of a lithium secondary battery using an electrolytic solution consisting of manganese dioxide as a positive electrode, metallic lithium as a negative electrode, and a non-aqueous solvent. 1 is a case that also serves as a positive electrode terminal, 2 is a grappling plate that serves as a wound terminal, 3 is a polyderobey gasket that insulates the case and the sealing plate, and 4 is a positive electrode, which is made of manganese dioxide 85 heavy corrosion part and conductive material. 10 parts by weight of acetylene black and 5 parts by weight of polytetrafluoroethylene as a binder were kneaded to a thickness of 0.7 mf)v-}
After shaping it into a shape, it was punched out to a diameter of 15.0 mm. Thereafter, it was vacuum-dried at a high temperature and crimped onto the positive electrode current collector 5 that had been welded to the case 1 in advance. 6 is metallic lithium,
It was crimped to the negative electrode current collector 7 with a thickness Q of 4 ms and a diameter of 161111.

8 is a sebarator made of polyderobylene m microporous membrane ● The electrolyte was a mixture of 5 types of 10, DEO, and 2Me-THF, and the mixing ratio was 2:1 73.
As a solute, a solution of 1 mo/I//l of lithium perchlorate (LiOl04) was used.

The following two types of tests were conducted on the battery ▲ produced in this manner.

CYCLE test Test temperature I + 25℃, charge + running current 0.5m▲, final voltage 3.5V discharge;
Constant current 1.01lA, final voltage 2.4v Low temperature discharge test test temperature! -20℃ Two-way discharge current 1.0jll▲ The solvent of the comparative electrolyte was Xa and 2Me-TH? , Battery B was prepared in the same manner as in the Super Dormitory Example except that the mixing ratio was 111, and the test was conducted in the same manner.

FIG. 2 shows the results of the cyclotviK experiment. As is clear from FIG. 2, it can be seen that battery A exhibits the effects of the present invention with less decrease in capacity than battery B.

FIG. 3 shows the discharge characteristics of batteries A and B at -20°C. Battery A has a larger discharge capacity at low temperatures than battery B. This shows that the present invention has excellent discharge characteristics at low temperatures.

Effects of the Invention As described above, the present invention can provide a lithium secondary battery with improved charge/discharge characteristics and discharge characteristics at low levels of solder, and therefore has extremely great industrial value.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a lithium secondary battery according to an embodiment of the present invention, and FIGS. 2 and 5 are characteristic comparison diagrams of a battery of the present invention and a conventional battery. 1... Case 2... Sealing plate 5... Gasket 4... Positive electrode 5... Positive electrode current collector 6... Negative electrode 7... Negative electrode S electric body 8... Sebarator

Claims (1)

[Claims] It is equipped with a negative electrode containing lithium as an active material, a positive electrode, and an electrolytic solution consisting of an organic solvent in which a lithium salt is dissolved. 1,2
- dimethoxyethane, and 4-methyl-1,3-dioxolane.