Modifying an ultrathin insulating layer to suppress lithium dendrite formation within garnet solid electrolytes

Abstract

The electronic conductivity of solid electrolytes, which plays an important role in inducing Li dendrite deposition, is a key obstacle to the practical application of Li metal in all-solid-state lithium metal batteries. Herein, an ultrathin insulating LiF coating with controllable thickness is proposed as an electronic isolation layer to inhibit the formation of Li dendrites. The homogeneous LiF interfacial layer can effectively facilitate the physical contact of the Li metal and LLZTO electrolyte and promote uniform Li plating/stripping. In contrast to the inhomogeneous lithium nucleation and dendritic lithium growth in an unmodified LLZTO electrolyte induced by electron beam irradiation, dendritic Li deposition is efficiently inhibited on LiF coated LLZTO. The Li|0.5LF-LLZTO|Li symmetric cell exhibits a low interfacial impedance of 12.7 ohm cm² and stable Li plating/stripping without lithium penetration, over 1500 hours at 0.2 mA cm⁻² and 300 hours at 0.4 mA cm⁻². Besides, the Li|0.5LF-LLZTO|LiCoO₂ full cell also shows excellent long-term cycling stability with a high capacity retention of 76.8% after 2500 cycles at 1C. Our results reveal the importance of tuning the interface modification layer properties to guide the uniform lithium plating toward suppressing Li dendrite formation in solid electrolytes.