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.