Designing phosphazene-derivative electrolyte matrices to enable high-voltage lithium metal batteries for extreme working conditions

The current high-energy lithium metal batteries are limited by their safety and lifespan owing to the lack of suitable electrolyte solutions. Here we report a synergy of fluorinated co-solvent and gelation treatment by a butenoxycyclotriphosphazene (BCPN) monomer, which facilitates the use of ether-based electrolyte solutions for high-energy lithium metal batteries. We show that the safety risks of fire and electrolyte leakage are eliminated by the fluorinated co-solvent and fireproof polymeric matrices. The compatibility with high-energy cathodes is realized by a well-tailored Li⁺ solvation sheath, along with BCPN-derived protective surface films developed on the cathodes. Our Li | |LiNi_0.8Co_0.1Mn_0.1O₂ cells reach high-capacity retention, superior low-temperature performance, good cyclability under high pressure and steady power supply under abusive conditions. Our electrolyte design concept provides a promising path for high energetic, durable and safe rechargeable Li batteries.