High-conductivity open framework fluorinated electrolyte bonded by solidified ionic liquid wires for solid-state Li metal batteries

Solid-state Li metal batteries are considered as the promising electrochemical energy storage devices of next generation in view of their safety and high energy density. Solid electrolyte as the critical part often fails to meet the requirements of electrochemistry and stability and degrades the performance of solid state batteries. The explorations of new solid-state electrolyte prototypes and their tailored synthesis strategies are of important significance. Fluoride solid electrolytes are expected to possess the advantages of air stability and Li dendrite inhibition, however their low ion conductivity (10−6-10−7 ​S/cm at room temperature) is still a short slab. In this work, we report a low-temperature ionic liquid method to synthesize nanostructured Li-rich fluoride solid electrolyte Li3GaF6, which is characterized by open-framework structured grains and ionic liquid decorated grain boundaries. The ionic liquid is solidified into nano-floccule and acts as in-situ binder to cement surrounding nanoparticles and the whole electrolyte pellet, retarding its powdering and cracking especially at the contact interfaces with electrodes during cycling. Benefiting from the enhancement of interfacial ion transport, the optimized Li3GaF6 achieves the highest record of ionic conductivity (close to 10−4 ​S/cm at room temperature) among fluoride solid electrolytes. A solid-state Li/Li3GaF6/LiFePO4 cell is successfully driven for at least 150 cycles at 1 ​C. The structure dissection and nanostructure adjustability of fluoride solid electrolytes as well as their interface modification can pave an alternative way to the activation of solid state batteries.