JPH09180760A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery, which can prevent the generation of expansion and bursting of a battery whose reliability and safety are improved, by exposing a part of the surface of a negative electrode and a positive electrode which can store and discharge the lithium, from the separator, and arranging both exposed surfaces so as to be displaced from each other. SOLUTION: A positive electrode 1, which contains LiCoO2 or the like, is formed on a collector 4 formed of an aluminum foil or the like. On the other hand, a negative electrode 2 containing carbon, the oxide of transition metals or the chalcogen material, which can store and discharge lithium, is formed on a collector 5 formed of a copper foil or the like. These positive electrode 1 and negative electrode 2 are arranged through a separator 3, which is impregnated with the electrolyte such as LiPF6 , or the organic solid electrolyte, which contains the electrolyte, so as to form a nonaqueous secondary battery. At this stage, a part of the surface of each positive electrode and negative electrode is not coated with the separator, and the surfaces 7, 8 exposed from the electrolyte are arranged so as to be displaced from each other. With this structure, an expansion, which is generated by the initial charging, is eliminated by applying the constant voltage thereafter, and a danger of generation of a bursting is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery in which a negative electrode is made of carbon capable of inserting and extracting lithium, an oxide of a transition metal, and a chalcogenide, and an electrolyte is a non-aqueous electrolyte.

[0002]

2. Description of the Related Art Conventionally, a positive electrode and a negative electrode have been covered with an entire surface separator and immersed in an electrolyte.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention At the time of charging in the first cycle, CH ₄ , C ₂ H ₆ ,
Since CO 2 gas and a small amount of water contained as impurities in the material are decomposed to generate H ₂ gas and the internal pressure of the battery increases,
There is a problem that the battery is ruptured and that the prismatic or flat battery swells. In the past, to prevent these problems, the internal pressure of the battery case was increased by using a pressure-resistant structure, but with prismatic and flat batteries, the mechanical strength of the battery container is insufficient and bulging must be prevented. Was difficult.

[0004]

According to the present invention, a separator and a portion not covered with an electrolyte are arranged on a part of the working surface of each of the positive electrode and the negative electrode. In a cell having such an electrode, it was found that the gas once generated is absorbed when a constant voltage is continuously applied in the charging direction.

Although the mechanism of gas absorption is not clear,
It is presumed that the voltage disappears due to electrochemical oxidation reaction and reduction reaction of the accumulated gas on the exposed positive and negative electrode surfaces.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A separator and an exposed portion not covered with an electrolyte are provided on a part of the surfaces of a positive electrode and a negative electrode. By applying a constant voltage to the battery having such a structure in the charging direction, the swelling of the battery, which is considered to be caused by the gas generated during the first charging, is eliminated.

(Invention 1) 90 parts by weight of lithium cobalt oxide having an average particle size of 10 μm and Ketchin black (hereinafter referred to as KB
5 parts by weight of polyvinylidene fluoride N
Add 50 parts by weight of a 10% solution of methyl-pyrrolidone (hereinafter referred to as NMP) and knead. The kneaded material is applied onto the aluminum foil current collector 4, dried, and pressed to obtain the positive electrode 1. Here, FIG. 1 is a cross-sectional view of the non-aqueous secondary battery of the present invention.

Coke-based carbon particles 9 having an average particle size of 15 μm
5 parts by weight of polyvinylidene fluoride NMP 10% solution 5
0 part by weight is added and kneaded, coated on the copper foil current collector 5, dried, and pressed to obtain the negative electrode 2.

Reference numeral 3 is a separator made of a polyethylene microporous film. LiPF ₆ is formed from ethylene carbonate (hereinafter referred to as EC) and diethyl carbonate (hereinafter DE).
(C) is impregnated with an electrolyte solution. The electrolytic solution is also impregnated in the positive electrode 1 and the negative electrode 2.
Reference numerals 7 and 8 are non-opposing portions provided on part of the surfaces of the positive electrode and the negative electrode, and are not covered with the separator 3 and are exposed.

When this battery was charged for the first time at a current density of 0.5 mA / cm ² , a temporary swelling due to gas generation inside the battery was observed, but a constant voltage of 4.2V. Was applied in the charging direction, the swelling disappeared, and no swelling was observed even after repeated charging and discharging.

(Invention 2) In FIG. 1, the separator portion contains LiPF ₆ as an electrolyte and EC /
A cross-linked polyethylene oxide polymer solid electrolyte containing DEC was placed. The other configurations are the same as those of the first embodiment. Exposed portions 7 and 8 not covered with the solid polymer electrolyte were provided on part of the surfaces of the positive electrode and the negative electrode. Under the same conditions as in Example 1,
The first charge was performed. Some swelling was observed during charging, but the swelling disappeared when a constant voltage of 4.2 V was applied as in Example 1.

(Comparative Example 1) As shown in FIG. 2, the constitution was the same as that of the invention 1 except that non-facing exposed portions were not provided on a part of the surfaces of the positive electrode and the negative electrode. The first charging was performed with the entire surfaces of the positive electrode and the negative electrode facing each other. Swelling of the battery due to gas generation was observed during charging. Invention 1 of the present battery
Similar to the above, the swelling did not disappear even when a voltage of 4.2 V was applied. Further, after repeated charging and discharging, the swelling gradually increased.

(Comparative Example 2) In FIG. 2, as in the case of the present invention 2, a solid polymer electrolyte was placed in the separator portion. The surfaces of the positive electrode and the negative electrode were covered with an electrolyte to eliminate exposed parts. As in Comparative Example 1, swelling occurred on the first charge, and the swelling did not disappear even after a constant voltage of 4.2 V was applied, the internal impedance of the battery increased, and subsequent charge / discharge became impossible. .

[0014]

According to the present invention, a non-aqueous secondary battery in which the negative electrode is made of carbon or a transition metal oxide or chalcogenide capable of absorbing and desorbing lithium decomposes the electrolytic solution during the first cycle charging. It has a function of absorbing the gas generated by the gas, can prevent the battery from swelling and bursting, and is effective for improving the reliability and safety of the battery.
It has high industrial value.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a non-aqueous secondary battery of the present invention.

FIG. 2 is a cross-sectional view of a conventional non-aqueous secondary battery.

[Description of Reference Signs] 1 positive electrode 2 negative electrode 7 non-opposing surface provided on positive electrode 8 non-opposing surface provided on negative electrode

Claims (2)

[Claims] 1. A carbon whose negative electrode is capable of inserting and extracting lithium,
A non-aqueous secondary battery made of a transition metal oxide or chalcogenide, wherein a part of the surfaces of the negative electrode and the positive electrode are not covered with a separator and do not face each other, and the non-facing surface is an electrolyte. A non-aqueous secondary battery, which is exposed from. 2. The non-aqueous secondary battery according to claim 1, wherein the electrolyte is an organic polymer solid electrolyte.