An energy storage element, wherein a non-aqueous electrolyte contains lithium difluorobis(oxalato)phosphate that is a first additive represented by Formula (1): and lithium tetrafluorooxalatophosphate that is a second additive represented by Formula (2): wherein the amount of the first additive to be added is not less than 0.3% by weight and not more than 1.0% by weight based on the total weight of the non-aqueous electrolyte, and the amount of the second additive to be added is not less than 0.05 times and not more than 0.3 times the amount of the first additive to be added.