Three-dimensional hierarchical composite polymer electrolyte with enhanced interfacial compatibility for all-solid-state lithium metal batteries

Composite polymer electrolytes (CPEs) are regarded as promising candidates for high-energy-density all-solid-state lithium metal batteries (ASSLMBs) because they combine the merits of solid polymer electrolytes and inorganic solid electrolytes. However, poor electrode/electrolyte interface compatibility and filler agglomeration limit their practical application. In this study, an in-situ polymerization method was used to create a three-dimensional (3D) hierarchical CPE using 3-(trimethoxysilyl)propyl methacrylate (KH570)-modified Li6.4La3Zr2Al0.2O12 (KH@LLZO) particles. The KH@LLZO-rich (up to 80 wt%) region of the electrolyte provides a rigid barrier to prevent lithium dendrite growth, while the other region of the electrolyte with an appropriate KH@LLZO content (8 wt%) achieving optimal ionic conductivity infiltrates into the entire battery system to allow for smooth Li+ transport. The symmetric Li|Li cell exhibits steady lithium plating/stripping cycling over 600 h at 0.3 mA h cm−2 and has a decent critical current density of 0.9 mA cm−2. This is made possible by the elaborate structure of the electrolytes. Full Li|LiFePO4 cells have preferable cycling stability (capacity retention of 91.6% after 200 cycles at 0.5 C). Moreover, pouch cells that use the in-situ-formed electrolyte exhibit excellent flexibility and safety. This novel design of 3D hierarchical CPEs using surface-modified LLZO particles paves the way for the development of dendrite-free and high-performance ASSLMBs.