NONAQUEOUS ELECTROLYTE ENERGY STORAGE DEVICE, AND METHOD FOR MANUFACTURING NONAQUEOUS ELECTROLYTE ENERGY STORAGE DEVICE

An aspect of the present invention is a nonaqueous electrolyte energy storage device including: a positive electrode including a positive composite layer containing a transition metal oxide and a boron element; a negative electrode; and a nonaqueous electrolyte containing a sulfate compound, in which the content of the boron element in the positive composite layer is 0.03% by mass or more.