NONAQUEOUS ELECTROLYTE ENERGY STORAGE DEVICE AND METHOD FOR PRODUCING THE SAME

Provided are a nonaqueous electrolyte energy storage device having high capacity retention ratio after charge-discharge cycles at a high temperature of about 45° C., and a method for producing such a nonaqueous electrolyte energy storage device. One aspect of the present invention is a nonaqueous electrolyte energy storage device including a positive electrode having a positive composite that contains a phosphorus atom and a lithium-transition metal composite oxide containing manganese, wherein, in a spectrum of the positive composite by X-ray photoelectron spectroscopy, a peak position for P2p is observed at 134.7 eV or less. Another aspect of the present invention is a method for producing a nonaqueous electrolyte energy storage device, the method including forming a positive electrode using a positive composite paste that contains a phosphorus oxo acid and a lithium-transition metal composite oxide containing manganese.