Functional ternary salt construction enabling an in-situ Li3N/LiF-enriched interface for ultra-stable all-solid-state lithium metal batteries

Poly(ethylene oxide)-based polymer all-solid-state lithium metal batteries (ASSLBs) have received widespread attention due to their low cost, good process ability, and high energy density. Nevertheless, the growth of Li dendrites within polymer solid-state electrolytes damages the reversibility of Li anodes and still impedes their widespread application. One efficient strategy is to construct a superior solid electrolyte interface. Herein, a stable interface enriched with Li₃N and LiF is in-situ formed between Li anode and a ternary salt electrolyte. This ternary salt electrolyte is innovatively designed by introducing lithium bis(trifluoromethane sulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and LiNO₃ to poly(ethylene oxide) matrix. Surface characterization indicates that LiNO₃ and LiFSI contribute to forming a Li₃N-LiF-enriched interface and meanwhile LiTFSI ensures excellent conductivity. Theoretically, among various Li compound components, Li₃N has high ionic conductivity, which is beneficial for reducing overpotential, while LiF has high interfacial energy which can enhance nucleation energy and suppress the formation of Li dendrites. The experimental results show that ASSLBs coupled with LiFePO₄ cathode display extremely excellent cycle stability approximately 2200 cycles at 2 C, with a final and corresponding discharge specific capacity of 96.7 mA h g⁻¹. Additionally, a schematic illustration of the working mechanism for the Li₃N-LiF interface is proposed.