Bulk-to-interface fluorination for stable and low-pressure all-solid-state lithium metal batteries

All-solid-state lithium metal batteries are widely considered promising next-generation energy storage systems owing to high specific energy and enhanced safety. However, their practical deployment is hindered by high stack pressure and inferior electrochemical performance. Here, we exploit the fast thermodynamic diffusion of fluorine atoms to design a core-shell structured sulfide electrolyte, Li_5.4PS_4.4Cl_1.4F_0.2-0.2LiF, featuring 50 nm LiF nanoshell and F-enriched bulk. During electrochemical operation, fluorine atoms diffuse into the LiNi_0.83Co_0.12Mn_0.05O₂ positive electrode lattice, enhancing structural robustness and mitigating mechanochemical failure, while the LiF nanoshell stabilizes both the Li metal negative electrode and positive electrode interfaces through spontaneous fluorination diffusion. As a result, full cells demonstrate good electrochemical performance, including long cycle life, high-voltage stability, and robust operation across a wide temperature window. Furthermore, all-solid-state pouch cells operated under a low stack pressure of 2.5 MPa exhibit stable cycling over 350 cycles (1 C) with 85% capacity retention, and achieve a high specific energy of over 400 Wh/kg (based on solid electrolyte, Li metal, and positive electrode materials). This bulk-to-interface fluorination strategy effectively mitigates mechanochemical failures, offering an alternative pathway toward low-pressure, long-life, and high-energy all-solid-state batteries.