A surface sulfurization strategy for tuning the lithiophilicity of garnet electrolyte pellets towards advanced solid-state lithium metal electrolyte†

Garnet solid-state electrolytes (SSEs) have extraordinary application prospects due to their high room temperature ionic conductivity and high stability to lithium metal. However, when exposed to air during the preparation process, contaminants are inevitably generated on the electrolyte surface, resulting in poor wettability of the Li/garnet interface and high interfacial resistance. Moreover, solid-state batteries assembled with contaminated electrolytes can easily lead to the formation and expansion of lithium dendrites. Herein, we demonstrate a surface chemistry strategy of rapid vulcanization treatment to improve interface problems by introducing lithium sulfides into the garnet electrolyte. Compared to the surface contaminants (e.g., Li₂CO₃) on garnet, lithium sulfides (e.g., Li₂S) have several advantages; it is a good Li⁺ conductor and has good wettability to both the garnet surface and Li metal anode. The interfacial resistance of the vulcanized garnet-SSE pellets decreased from 2961 Ω cm² for LLZT@LC to 391 Ω cm² for LLZT@LS. In addition, the lithium symmetric battery assembled by using LLZT@LS pellets exhibits stable plating/stripping cycling performance and ultralow overpotential at a current of 0.2 mA cm⁻² without Li dendrite growth. Moreover, the LiFePO₄/Li batteries with LLZT@LS pellets show excellent rate performances and cycling stability (114.3 mA h g⁻¹ @ 0.5C after 150 cycles) with a capacity retention of 86%. These results demonstrate that the rapid treatment of garnet contaminants by a surface chemistry strategy is not only a simple and efficient solution but also provides strong support for the realization of high-performance solid-state lithium metal batteries (SSLMBs).