Hydrofluoric-fixation separators through hydrogarnet electrolyte bonded by silane for long-cycling lithium metal batteries

Lithium metal batteries (LMBs) with high-voltage cathodes easily suffer from electrode structure degeneration caused by hydrogen fluoride (HF) attack, especially in electrolytes with high moisture content. Herein, we report a hydrofluoric-fixation bifunctional separator, in which 3-aminopropyltriethoxysilane (APTES) - modified hydrogarnet electrolyte (Li_1.5La₃Zr_1.5Ta_0.5O₇(OH)₅) serves as a functional layer on a polypropylene (PP) separator surface. The silane acts as fixation sites for HF via Si-F bond formation, effectively eliminating HF in the electrolyte and inhibiting cathode degradations. Simultaneously, the hydrogarnet electrolyte enhances lithium-ion transfer kinetics owing to its high ionic conductivity, leading to suppressions of lithium dendrites. As a result, symmetric Li cells employing PP@LH-A separators exhibit stable cycling for 2000 h at 5 mA cm^-2. Li/LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cells possess a capacity retention rate of 78.2 % at 2 C after 500 cycles, even in the electrolytes containing 500 ppm of water. This strategy offers a promising approach for HF fixation in high-voltage lithium metal batteries.