LITHIUM ION SECONDARY BATTERY

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery superior in life characteristic.SOLUTION: A lithium ion secondary battery comprises, in a battery container, a positive electrode, a negative electrode and a separator, and an electrolyte solution. The electrolyte solution contains a cyclic sulfate ester represented by the formula (I) below, and tris phosphate (trimethylsilyl). As a negative electrode active material, an easily graphitizable carbon is included. The cyclic sulfate ester is contained at 0.3-1.6 mass% to a total amount of the electrolyte solution, and the tris phosphate (trimethylsilyl) is contained at 0.1-0.8 mass% to the total amount of the electrolyte solution.SELECTED DRAWING: Figure 1 【課題】寿命特性に優れたリチウムイオン二次電池を提供する。【解決手段】正極、負極およびセパレータと、電解液と、を電池容器内に備えるリチウムイオン二次電池であって、前記電解液は、下記式（Ｉ）に示す環状硫酸エステル及びリン酸トリス（トリメチルシリル）を含み、負極活物質として易黒鉛化炭素を含み、前記環状硫酸エステルは、電解液の全量に対し０．３〜１．６質量％含み、前記リン酸トリス（トリメチルシリル）は、電解液の全量に対して０．１〜０．８質量％含むリチウムイオン二次電池。【選択図】 図１