Nippon Telegraph and Telephone Corporation

Toshiro Hirai

Jun-ichi Yamaki

Shigeto Okada

Takeshi Okada

Yoji Sakurai

Hideaki Ohtsuka

Shin-ichi Tobishima

Masayasu Arakawa

Kaoru Asakura

Jun-Ichi Yamaki

A capacity estimation method for a Li-ion cell is provided. In the method, according to a first aspect, an elapsed time from the time when charge voltage in constant current charge reaches a predetermined voltage to the time when charge condition is changed to a constant voltage mode is used for calculating an estimated capacity of said Li-ion cell. According to a second aspect, a charge current after a lapse of a predetermined time from the time when charge condition is changed to a constant voltage mode is used. According to a third aspect an elapsed time from the time when charge condition is changed to a constant voltage mode to the time when charge current becomes &agr; (0<&agr;<1) times is used.

Capacity estimation method, degradation estimation method and degradation estimation apparatus for lithium-ion cells, and lithium-ion batteries

The present invention provides an electrolyte for use on a secondary lithium battery comprising amorphous V.sub.2 O.sub.5 base cathode active material, a metallic lithium base active material, and an electrolytic solution lithium salt dissolved in a mixed organic solvent. The organic solvent is ethylene carbonate mixed with one organic solvent of 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 1,3-dioxalan, 4-methyl-1,3-dioxalan, 1,2-dimethoxyethane, etc. The mixed ratio of ethylene carbonate ranges within 10 to 50%, and water content of the electrolytic solution ranges within 400 to 5 ppm, and the content of impurities other than water ranges within 1000 to 10 ppm. The resultant secondary lithium battery is excellent in charge-discharge cycle life.

Secondary lithium battery

A lithium battery essentially consisting of an amorphous cathode active material mainly composed of V.sub.2 O.sub.5 and prepared by adding with at least one first additive selected from the group consisting of P.sub.2 O.sub.5, TeO.sub.2, GeO.sub.2, Sb.sub.2 O.sub.3, Bi.sub.2 O.sub.3 and B.sub.2 O.sub.3 and/or at least one second additive selected from the group consisting of MoO.sub.3 and WO.sub.3, heating to melt the admixture and then quenching the molten admixture; an anode active material made of metallic lithium or a lithium alloy; and an electrolyte made of a mixture of a aprotic solvent and a lithium salt. The battery is a small-sized and light-weight secondary battery having a high energy density and being improved in charge-discharge cycle lifetime.

Lithium battery including vanadium pentoxide base amorphous cathode

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Mito, Japan

Toshiro Hirai