Origin of Lithiophilicity of Lithium Garnets: Compositing or Cleaning?

Abstract

Garnet-type Li6.5La3Zr1.5Ta0.5O12 (LLZTO), a promising solid-state electrolyte, is reported to exhibit lithiophobicity. Herein, it is demonstrated that the origin of the lithiophobicity is closely related to the surface compositions of both the lithium and LLZTO. Surface impurities with high melting points such as Li2O, Li2CO3, LiOH, or LiF inhibit the wettability between lithium metal and LLZTO, and the widely adopted compositing strategy may improve the wettability by merely breaking the surface impurity layers. A simple but effective “polishing-and-spreading” strategy is proposed to remove the surface impurities and obtain clean Li/LLZTO interfaces. Thus, a tight and continuous Li/LLZTO interface with an interfacial resistance of 17.5 Ω cm2 is achieved, which leads to stable cycling of the symmetric Li cells and a critical current density up to 2.8 mA cm–2. This work provides a new perspective to understand the lithiophilicity of garnet-type electrolytes and contributes to designing robust Li/garnet interfaces.By comparing the wetting effect of different Li-based composite anodes, and using a “polishing-and-spreading” strategy, lithium garnet is demonstrated to well wet Li, rendering a Li/LLZO interfacial impedance of 17.5 Ω cm2 and a critical current density of 2.8 mA cm–2, without using any intermediate layer or compositing.