In Situ Coating Li3PO4 on Li6.5La3Zr1.5Ta0.5O12 Achieving Lithium Dendrites Inhibition and High Chemical Stability

Abstract

Solid-state electrolyte (SSE) is a potential way to solve the safety problems of lithium metal batteries (LMBs), and Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) is one of the most extensive research SSEs due to its good air stability and wide electrochemical window. However, the residual alkali on LLZTO surface limits its application with polyvinylidene difluoride (PVDF)-contained binders, and the uncontrollable lithium dendrites growing between the grain boundaries of LLZTO particles would lead to rapid capacity fading and potential short circuit risk. Herein, by in situ coating Li₃PO₄ (LPO) on LLZTO particles (LLZTO@LPO) evenly, the residual alkali on the LLZTO surface is neutralized and the pH value is reduced to 8.84. The modified LLZTO can be mixed with PVDF solution and shows good fluidity without a cross-linking reaction, making the subsequent ceramic coating on the separator feasible. The LLZTO@LPO coating polyethylene (PE) separator can achieve 1400 h (115% increase) stable cycling under 1 mA cm⁻² current density in the Li∥Li symmetrical cell and 80% capacity retention after 260 cycles (NCM622-Li coin cell with 3 mAh cm⁻² loading). Furthermore, the LLZTO SSE pellets were prepared with the LLZTO@LPO and assembled in coin cell. The critical current density (CCD) result increases from 0.7 to 1.6 mA cm⁻² owing to that the LPO coating effectively inhibits the lithium dendrites formation through LLZTO grain boundaries. This work provides a strategy for fabricating the coating layer on LLZTO to improve the stability of LMBs.