Enhancing the Interfacial Ionic Transport via in Situ 3D Composite Polymer Electrolytes for Solid-State Lithium Batteries

Solid-state electrolytes with high ionic conductivity, excellent interfacial stability, and fast interfacial charge transport are desired for next-generation high-energy-density lithium–metal batteries. Herein, an in situ three-dimensional (3D) composite polymer electrolyte (CPE) is designed and fabricated by a simple solidification of poly(ethylene oxide) (PEO) solution precursor with a 3D TiO2 backbone on the cathode. The 3D CPE not only shows a very stable structure and high ionic conductivity but also exhibits impressive capability to suppress the Li dendrite growth. Moreover, the in situ built 3D CPE guarantees a tight and stable contact at the cathode/electrolyte interface, leading to an reduced interfacial resistance and polarization. Thus, in the solid-state Li||3D CPE||LiFePO4 batteries, the diffusion coefficient of Li+ ions has been increased by nearly 1 order of magnitude. The specific capacity (159 mAh g–1 at 20 mA g–1), rate capability, and cycling stability (85.1% capacity retention after 100 cycles) have also been significantly improved. This study provides an efficient strategy to reduce the interfacial resistance and improve the Li+ transport in solid-state batteries.