Boosting Li-Ion Conductivity of Fluoride Solid Electrolyte by Low-Temperature Molten Salt Ablation and Particle Boundary Doping
Xianhui Nie, Lei Meng, Jiulin Hu, Chilin Li
Abstract
Halide solid electrolytes (SEs) are attracting great attention, owing to their high ionic conductivity and excellent high-voltage compatibility. However, severe moisture sensitivity, poor thermal stability, and instability at the lithium metal anode interface with chloride and bromide SEs retard their applications in solid-state lithium metal batteries. Fluoride SEs are expected to solve these problems, but they are now plagued by inadequate room-temperature (RT) ionic conductivity. Herein, a low-temperature molten salt (LiCl+1.33AlCl 3 ) ablation method is proposed to enhance the ionic conductivity of monoclinic Li 3 GaF 6 by particle boundary doping. The RT ionic conductivity of Li 3 GaF 6 is correspondingly increased by 2 orders of magnitude, and the conductivity reaches 10 –4 S cm –1 at 60 °C. The improved ionic conductivity benefits from the enhancement of interfacial ion transport, with the formation of more conductive chlorine-doped Li 3 GaF 6– x Cl x and in situ binder LiAlCl 4 to cement surrounding nanoparticles. The as-synthesized Li 3 GaF 6 demonstrates outstanding humidity tolerance without conductivity degradation after exposure to a relative humidity of up to 35%. It also exhibits the widest electrochemical stability window experimentally (close to 6 V) compared with other state-of-the-art SEs. The solid-state Li/Li 3 GaF 6 /LiFePO 4 cell with a stable Li + -conductive polymer interface is successfully driven for at least 200 cycles at 0.5C. Our study provides a solution to various chemical and electrochemical stability issues encountered by the halide SE family.