Electrolytic solution for non-aqueous type battery and non-aqueous type secondary battery

Abstract

In a rechargeable non-aqueous electrolyte secondary battery using positive electrodes, negative electrodes and a non-aqueous electrolytic solution, additives to the electrolytic solution are used in combination, preferably in combination of at least two compounds selected from o-terphenyl, triphenylene, cyclohexylbenzene and biphenyl, and thus there are provided batteries excellent in safety and storage characteristics.

Description

[0001] The present invention relates to a non-aqueous electrolytic solution which can ensure safety of batteries at the time of overcharging with improving recovery characteristics of the batteries after storage at high temperatures, and to a non-aqueous type secondary battery using said electrolytic solution.[0002] Recently, AV devices and electronic devices such as personal computers of portable or cordless type have been rapidly developed, and secondary batteries which are small in size, light in weight and high in energy density are earnestly demanded as electric sources for driving these devices. Among them, non-aqueous electrolytic solution secondary batteries using a negative electrode containing lithium as an active material are hopefully expected as batteries having high voltage and high energy density.[0003] In the above batteries, lithium-containing metal oxides which show a voltage on the order of 4 V are used for positive electrode active materials, and materials capabl...

AI Technical Summary

Benefits of technology

[0011] In the case of adding to the batteries the above-mentioned additives such as aromatic compound having a methoxy group and a halogen group, biphenyl or thiophene, and an aromatic ether compound, it has been confirmed that in the generally used current ranges, the additives polymerize on the electrodes in overcharged state, and the safety is improved.

[0015] The present invention solves the above problems and to provide a battery excellent in high-temperature storage characteristics while ensuring the safety at overcharging.

[0016] In order to solve the above problems, according to the present invention, in a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent, two or more organic compounds differing in oxidative polymerization reaction potential are added. Preferably, organic compounds of relatively low oxidation reaction potential are added in a very small amount, preferably not less than 0.01% by weight and less than 1.0% by weight based on the total amount of the electrolytic solution, thereby to control the recovery characteristics after storage and the safety during overcharging. Specifically, it is preferred to add at least two organic compounds selected from o-terphenyl, triphenylene, cyclohexylbenzene and biphenyl.

[0022] These organic compounds are particularly effective when the positive electrodes comprise a material containing a lithium-containing metal oxide and the negative electrodes comprise a material containing graphite, and the non-aqueous electrolytic solution exerts the higher effect when it is an electrolytic solution in which a lithium salt as a solute is dissolved in a non-aqueous solvent mainly composed of a cyclic carbonate and a chain carbonate.

Problems solved by technology

When overcharging is carried out at such a current value, the safety cannot be sufficiently ensured.

If the setting is made so that the resistance increases in the generally used current region, naturally the inherent performance of the batteries are damaged.

However, it has been found that these additives must be added in an amount of not less than 1% by weight for ensuring the safety at the time of overcharging, but if the additives are added in a large amount, in an shelf life test, for example, an environment test (80.degree. C.) which supposes the case of leaving them in a car in summer, these additives partially react to cover the active material, resulting in considerable deterioration of the battery characteristics.

The above phenomenon is considered to occur because oxidative polymerization potential of the additives lowers due to exposure of the battery to a high temperature environment, and, furthermore, the potential distribution in the charged electrode is not uniform and higher potential portions are partially present, and, as a result, the additives react even in the ordinary environment of potential at which battery is used.

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