Lithium Metal Batteries with a Bone-Inspired Solid-Sol Electrolyte Based on Natural CaF₂

Inspired by the perfect integration of structure and function in mammalian bone, a general strategy for achieving high performance solid-sol electrolyte in lithium metal batteries is developed by utilizing naturally abundant calcium fluoride (CaF₂) as the inorganic matrix. With a small amount of organic solvent (only 12.8 wt %), a continuous ion transport network is established through multilevel nonbonding interactions between inorganic CaF₂ and organic solvent. While CaF₂ matrix offers excellent stability and robust mechanical support, the organic electrolyte network ensures high ionic conductivity and intimate interfacial contact. Furthermore, an integrated solid-electrolyte interphase enriched with LiF and Li-Ca alloy is generated via in situ reaction between the CaF₂ matrix and Li, leading to remarkably enhanced interfacial reaction kinetics and greatly suppressed Li dendrite growth. Consequently, the solid-sol electrolyte exhibits a wide electrochemical window of 5.26 V and a high Li⁺ transference number of 0.77 at room temperature. When matching LiFePO₄ cathodes, the batteries enable stable cycling over 200 cycles even at elevated temperatures up to 100 °C. Also, the created solid-sol electrolyte based on inorganic CaF₂ displays an interesting flame-retardant property. Notably, this strategy demonstrates extensibility to diverse liquid electrolytes, allowing straightforward tuning of solid-sol electrolyte properties for targeted performance optimization.