Toyota Jidosha Kabushiki Kaisha

Kabushiki Kaisha Toyota Chuo Kenkyusho

Shigehiro Kawauchi

Yoshiaki Kikuchi

Tohru Shiga

Akihiko Koiwai

A lithium secondary battery exhibiting very high safety, which is ensured by restraining both the generation of flammable gas caused by the decomposition of an electrolyte, and the emission of oxygen from a positive active material even during overcharging. The lithium secondary battery includes a positive electrode of which an active material is a lithium transition metal composite oxide, a negative electrode of which an active material is a carbon material, and a nonaqueous electrolyte containing an organic solvent in which a lithium salt is dissolved. The nonaqueous electrolyte contains at least one kind of conductive polymer-forming monomers which have an alkyl group and is electrochemically polymerizable on the positive electrode within a battery operation voltage, and at least one kind of film-forming agents which electrochemically decompose within the battery operation voltage to form films on a surface of the negative electrode.

Lithium secondary battery

By finding a voltage difference &Dgr;V between the maximum value and the minimum value of voltage of each cell constituting a battery set and then combining the voltage difference &Dgr;V with current I passing through the battery set into a value pair and store a plurality of the value pairs, the relationship between the voltage difference &Dgr;V and the current I is a relation represented by a straight line with the slope &Dgr;R thereof corresponding to an internal-resistance difference. Therefore, fault in the battery set can be determined from the magnitude of the slope &Dgr;R computed by a least-squares method. Fault determination for a battery set is made more accurate because variations in electromotive force caused by charge-and-discharge patterns and by changes in temperature are canceled when the voltage difference &Dgr;V is determined.

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Aichi, Japan

Shigehiro Kawauchi