An object of the present invention is to provide a nonaqueous electrolyte battery which restrains swelling of the battery during high-temperature storage and is excellent in battery performance after storage.
The invention is characterized by a specific constitution of a nonaqueous electrolyte and a combination thereof with a positive active material having specific crystal structure and composition. Namely, it is characterized by a nonaqueous electrolyte battery containing a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the above nonaqueous electrolyte contains at least a cyclic carbonate having a carbon-carbon π bond and the above positive electrode contains a positive active material comprising a composite oxide represented by a composite formula: LixMnaNibCOcO2 (wherein 0≦x≦1.1, a+b+c=1, |a-b|<0.05, 0<c<1) and having an α-NaFeO2-type crystal structure.