Optimized CeO 2 Nanowires with Rich Surface Oxygen Vacancies Enable Fast Li‐Ion Conduction in Composite Polymer Electrolytes

Low‐cost and flexible solid polymer electrolytes are promising in all‐solid‐state Li‐metal batteries with high energy density and safety. However, both the low room‐temperature ionic conductivities and the small Li + transference number of these electrolytes significantly increase the internal resistance and overpotential of the battery. Here, we introduce Gd‐doped CeO 2 nanowires with large surface area and rich surface oxygen vacancies to the polymer electrolyte to increase the interaction between Gd‐doped CeO 2 nanowires and polymer electrolytes, which promotes the Li‐salt dissociation and increases the concentration of mobile Li ions in the composite polymer electrolytes. The optimized composite polymer electrolyte has a high Li‐ion conductivity of 5 × 10 −4 S cm −1 at 30 °C and a large Li + transference number of 0.47. Moreover, the composite polymer electrolytes have excellent compatibility with the metallic lithium anode and high‐voltage LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC) cathode, providing the stable cycling of all‐solid‐state batteries at high current densities.