In situ construction of a Li-Ag&LiF interface enables stable cycling of all-solid-state lithium-metal batteries.

Solid polymer electrolytes (SPEs) are regarded as promising candidates for developing high energy-density Li metal batteries because of their flexible processability and low cost. However, the application of SPEs is still inherently impeded by the mediocre ionic conductivity and unstable Li/electrolyte interface. In this work, the silver fluoride (AgF) additive is introduced to optimize the ionic conductivity of PEO and induce the formation of stable solid electrolyte interphase (SEI) layer between Li metal and SPEs interface, thereby inhibiting the growth of lithium dendrites. AgF can be complex with anions to promote the dissociation of Li+-TFSI- ion pairs, improving the mobility of Li+ ions, as confirmed by experimental and computational studies. Moreover, the AgF converses to LiF and Li-Ag alloys via in-situ electrochemical reaction with Li anode, which can not only prevent the Li metal from parasitic reactions, but also reduce the concentration gradient of Li+ ions. Hence, the Li|Li symmetric cell containing PEO-3 % AgF electrolyte demonstrates stable cyclability for 1800 h at 0.2 mA cm-2 (60 °C). When paired with a commercial LiFePO4 cathode, the resulting all-solid-state Li-metal battery delivers remarkable cyclic performance of 126.9 mAh g-1 after 400 cycles (0.5 C). This work provides a new approach for the development of composite solid-state electrolyte films and lithium metal anodes in all-solid-state batteries.