LITHIUM ION SECONDARY BATTERY

摘要

This lithium ion secondary battery is provided with: a negative electrode which contains particles which are formed from at least one material (below, referred to as the metal and/or metal oxide) selected from metals that can alloy with lithium and metal oxides that can occlude and release lithium ions and which have a 0.78 or greater average value of circularity, defined by the expression below: Circularity = 4πS/L2 (here, S: surface area of projected particle image, L: circumferential length of projected particle image); a positive electrode; and a single-layer, highly heat-resistant microporous resin film separator. This battery has the property of having a reduced self-discharge failure rate.