Covalent fixation of phosphorus-containing flame retardants in gel polymer electrolytes for interface-stable and high-safety lithium-ion batteries

A long-standing trade-off between fire safety and electrochemical performance in lithium-ion batteries arises from aggressive parasitic reactions between highly reactive flame retardants and electrodes. Herein, a phosphorus-fixed gel polymer electrolyte is constructed by covalently integrating 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) into a vinylene carbonate-pentaerythritol tetraacrylate copolymer network through phosphorus-hydrogen addition. Covalent fixation confines DOPO within the gel matrix, delivering intrinsic flame retardancy while circumventing detrimental phosphorus-related side reactions. The abundant polar O=P–-O moieties in DOPO not only promote lithium salt dissociation and provide additional coordination sites to facilitate rapid Li + transport, but also actively reshape the Li + solvation environment. Specifically, the DOPO-incorporated polymer tethers solvent molecules and restricts their entry into the primary coordination sheath, shifting the solvation equilibrium toward an anion‑dominated configuration. This solvation reconfiguration fosters LiF‑rich robust interphases on both electrodes, ensuring stable lithium deposition and exceptional oxidative stability. As a result, the as -prepared electrolyte achieves outstanding compatibility exceeding 3500 h against lithium anode, significantly enhanced cycling stability in LiFePO 4 , high-voltage LiNi 0.8 Co 0.1 Mn 0.1 O 2 and LiNi 0.9 Co 0.05 Mn 0.05 O 2 -based full cells, as well as remarkable tolerance to flame, physical damage, and high-temperature operation. This work establishes a new paradigm for high-safety lithium-ion batteries, where phosphorus-based solvation engineering secures durable electrode interfaces under demanding conditions. The safety-performance trade-off in lithium-ion batteries is overcome by covalently fixing phosphorus-containing flame retardants into a gel polymer electrolyte, which reshapes Li + solvation to form durable LiF-rich interphases for uniform Li deposition and high-voltage stability. Download: Download high-res image (117KB) Download: Download full-size image