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

Abstract

For the purpose of oxidation decomposition control of the polyether-based solid polymer electrolyte (SPE) in the high-voltage state, lithium phosphate (Li3PO4)-coated cathode (LiCoO2) powder was prepared via a mechanical coating technique. An all-solid-state lithium polymer secondary battery that used Li3PO4-coated LiCoO2 was prepared. By the oxidation suppression enabled by the Li3PO4 that was intervened between SPE and LiCoO2, 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 Li3PO4 on LiCoO2.