Secondary power source

A secondary power source comprising a positive electrode made mainly of activated carbon, a negative electrode made mainly of a carbon material capable of doping and undoping lithium ions and an organic electrolyte containing a solute of a lithium salt, wherein the lithium salt comprises LiN(SO2R) (SO2R) wherein each of R and R which are independent of each other, is a C1-6 perfluoroalkyl group except R=R=CF3.