LITHIUM ION SECONDARY BATTERY

摘要

Provided is a lithium ion secondary battery that has high capacity and that makes it possible to obtain excellent charge-discharge cycle characteristics. The lithium ion secondary battery is characterized in that: a negative electrode active material includes a material S containing a compound SiOX (wherein the atomic ratio x of O atoms to Si satisfies 0.5 ≤ x ≤ 1.5) that comprises Si and O as constituent elements thereof; a separator includes a porous membrane (I) comprising mainly a thermoplastic resin and a porous layer (II) comprising mainly a filler that has a heat resistance temperature of at least 150 °C; a positive electrode contains a metal oxide that is configured from Li and a metal M other than Li and that serves as a positive electrode active material; and when discharged at a discharge current rate of 0.1 C until the voltage reaches 2.0 V, the molar ratio (Li/M) of the Li and the metal M other than Li included in the positive electrode active material is 0.9-1.05.