| 摘要 |
PROBLEM TO BE SOLVED: To provide: a lithium ion secondary battery with high safety which is arranged to be able to prevent the thermorunaway by cutting off a current when being overcharged; and a positive electrode used for such a lithium ion secondary battery.SOLUTION: A positive electrode comprises a positive electrode first layer (2). The positive electrode first layer includes a binding material and thermally expandable microcapsules each having a shell which is decomposed by a high voltage at overcharge and a thermal expansion temperature of 130°C or lower. The binding material included in the positive electrode first layer (2) is not dissolved in a core material of the microcapsules. When arriving at the voltage, the thermally expandable microcapsules are partially decomposed, thereby releasing the core material. Therefore, at the rise in the temperature, the thermally expandable microcapsules are expanded thermally and in parallel, the core material released therefrom is explosively evaporated. As a result, the positive electrode first layer (2) is destroyed to suppress an excessive large current at overcharge and consequently, thereby preventing the thermorunaway. |
