Enhanced Surface Interactions Enable Fast Li Conduction in Oxide/Polymer Composite Electrolyte.

Li -conducting oxides are considered better ceramic fillers than Li -insulating oxides for improving Li conductivity in composite polymer electrolytes owing to their ability to conduct Li through the ceramic oxide as well as across the oxide/polymer interface. Here we use two Li -insulating oxides (fluorite Gd Ce O and perovskite La Sr Ga Mg O ) with a high concentration of oxygen vacancies to demonstrate two oxide/poly(ethylene oxide) (PEO)-based polymer composite electrolytes, each with a Li conductivity above 10  S cm at 30 °C. Li solid-state NMR results show an increase in Li ions (>10 %) occupying the more mobile A2 environment in the composite electrolytes. This increase in A2-site occupancy originates from the strong interaction between the O of Li-salt anion and the surface oxygen vacancies of each oxide and contributes to the more facile Li transport. All-solid-state Li-metal cells with these composite electrolytes demonstrate a small interfacial resistance with good cycling performance at 35 °C.