LITHIUM ION SECONDARY BATTERY

A lithium ion secondary battery that includes a positive electrode, a negative electrode, a separator, a nonaqueous electrolytic solution, and a PTC layer between a positive electrode mixture layer and a positive electrode current collector and/or between a negative electrode mixture layer and a negative electrode current collector, the PTC layer having a positive temperature coefficient of resistance. The PTC layer contains nonconductive filler particles, and the electronic resistance at 120° C. is equal to or more than 100 times the electronic resistance at room temperature.