Solid-state lithium batteries are widely considered as next-generation lithiumion battery technology due to the potential advantages in safety and performance. Among the various solid electrolyte materials, Li-garnet electrolytes are promising due to their high ionic conductivity and good chemical and electrochemical stabilities. However, the high electrode/electrolyte interfacial impedance is one of the major challenges. Moreover, short circuiting caused by lithium dendrite formation is reported when using Li-garnet electrolytes. Here, it is demonstrated that Li-garnet electrolytes wet well with lithium metal by removing the intrinsic impurity layer on the surface of the lithium metal. The Li/garnet interfacial impedance is determined to be 6.95 Ω cm 2 at room temperature. Lithium symmetric cells based on the Li-garnet electrolytes are cycled at room temperature for 950 h and current density as high as 13.3 mA cm −2 without showing signs of short circuiting. Experimental and computational results reveal that it is the surface oxide layer on the lithium metal together with the garnet surface that majorly determines the Li/garnet interfacial property. These findings suggest that removing the superficial impurity layer on the lithium metal can enhance the wettability, which may impact the manufacturing process of future high energy density garnet-based solid-state lithium batteries. are gratefully acknowledged for assisting with relevant experimental analysis. Center for High Performance Computing of SJTU is gratefully acknowledged for providing computational facilities for all the simulations. Conflict of InterestThe authors declare no conflict of interest.

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Garnet-type Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (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 Li 2 O, Li 2 CO 3 , 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 "polishingand-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 cm 2 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.

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Solid-state lithium batteries can improve the safety and energy density of the present liquid-electrolyte-based lithium-ion batteries. To achieve this goal, both solid electrolyte and lithium anode technology are the keys. Lithium garnet is a promising electrolyte to enable the next generation solid-state lithium batteries due to its high ionic conductivity, good chemical, and electrochemical stability, and easiness to scale up. It is relatively stable against Li metal but the poor contact area and the presence of resistive impurity or decomposition layers at the interface interfere with fast charge transfer, thereby, spiking the interfacial resistance, overpotential, local current density, and the propensity for dendrite growth. In this Review, we first summarize the recent understanding of the interfacial problems at the Li/garnet interface from both computational and experimental viewpoints while seizing the opportunity to shed light on the chemical/electrochemical stability of garnet against Li metal anode. Also, we highlight various interface optimization strategies that have been demonstrated to be effective in improving the interface performance. We conclude this Review with a few suggestions as guides for future work.