Alloying Interphase Engineering of Reusable MOF‐Based Solid Electrolyte for Ultrastable Lithium Metal Anodes

Coating the separator surface of high-energy-density lithium batteries with a solid-state inorganic ion conductor can enhance the ionic conductivity and lithium-ion transference number, while improving interfacial contact between the separator and electrodes. However, during battery cycling, high-valence metal ions in the solid-state ion conductor are prone to reduction by metallic lithium, leading to performance degradation. In this study, the applicability of inorganic solid-state electrolytes, such as Li₁.₃Al₀.₃Ti₁.₇(PO₄)₃ (LATP), compounded with Ag-MOF on the lithium metal anode side is investigated. Experimental results demonstrate that a composite separator with an Ag-MOF:LATP mass ratio of 8:92, when assembled in Li||Li symmetric cells, exhibits stable cycling for over 1200 h at 0.5 mA cm^-2. Furthermore, in NCM811||Li batteries, after 300 cycles at 0.5C and 500 cycles at 5C, the capacity retention rates remain at 70.9% and 76.1%, respectively. The functional mechanism of Ag-MOF involves formation of an Ag-Li alloy during cycling, which suppresses Ti⁴⁺ reduction and enhances cycling stability. The most significant finding is that the disassembled composite separator can be reused for two additional charge-discharge cycles after battery cycling, exhibiting outstanding reusability with a capacity retention rate consistently exceeding 70% after 500 cycles at 5C rate.