Fabrication of High-Voltage, High-Capacity All-Solid-State Lithium Polymer Secondary Batteries by Application of the Polymer Electrolyte/Inorganic Electrolyte Composite Concept

For the purpose of oxidation decomposition control of the polyether-based solid polymer electrolyte (SPE) in the high-voltage state, lithium phosphate (Li 3 PO 4 )-coated cathode (LiCoO 2 ) powder was prepared via a mechanical coating technique. An all-solid-state lithium polymer secondary battery that used Li 3 PO 4 -coated LiCoO 2 was prepared. By the oxidation suppression enabled by the Li 3 PO 4 that was intervened between SPE and LiCoO 2, charging up to a high voltage (4.6 V vs Li/Li + ) was made possible and the discharge capacity was observed to be over 200 mAh g - 1 . Detailed electrochemical analysis was enabled by a combination of constant current−constant voltage charging measurements and electrochemical impedance spectroscopy (EIS). As a result, it became clear that the oxidation decomposition that takes place at the SPE/cathode interface can be controlled by a coating of Li 3 PO 4 on LiCoO 2 .