Trifunctional DOPO‐Engineered Polypropylene Separator With Li⁺‐Concentrating Interfaces for High‐Safety Lithium‐Ion Batteries Under Extreme Conditions

A DOPO‐based cross‐linked polymer creates a multifunctional separator for lithium‐ion batteries. It concurrently addresses safety (flame retardancy, thermal stability) and performance (enhanced Li+ transport, capacity retention), pioneering a novel approach to high‐performance battery design. Abstract This study develops a cross‐linked polymer modified polypropylene (PP) separator for lithium‐ion batteries, using DOPO (9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide). The separator features surface‐rich polar functional groups (such as ‐NH2) and bonded structures (P‐O, P = O), enhancing Li+ ion migration via dipole‐dipole interactions. The modified separator demonstrates improved microstructural stability, thermal stability (>90 °C), and mechanical strength (>200 MPa). Batteries using this separator maintain excellent capacity retention (105.2 mAh g−1) after high‐temperature cycling (130 °C at 2C) and show good flame retardancy (self‐extinguishing). Density functional theory (DFT) calculations explain the Li+ enrichment mechanism and the separator's thermal/flame‐retardant properties. This work pioneers the multifunctional use of DOPO in lithium‐ion battery separators, combining flame retardancy, enhanced Li+ conductivity, and improved stability, offering a novel approach to producing safer, high‐performance separators for large‐scale applications. A DOPO-based cross-linked polymer creates a multifunctional separator for lithium-ion batteries. It concurrently addresses safety (flame retardancy, thermal stability) and performance (enhanced Li + transport, capacity retention), pioneering a novel approach to high-performance battery design. Abstract This study develops a cross-linked polymer modified polypropylene (PP) separator for lithium-ion batteries, using DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide). The separator features surface-rich polar functional groups (such as -NH 2 ) and bonded structures (P-O, P = O), enhancing Li + ion migration via dipole-dipole interactions. The modified separator demonstrates improved microstructural stability, thermal stability (>90 °C), and mechanical strength (>200 MPa). Batteries using this separator maintain excellent capacity retention (105.2 mAh g −1 ) after high-temperature cycling (130 °C at 2C) and show good flame retardancy (self-extinguishing). Density functional theory (DFT) calculations explain the Li + enrichment mechanism and the separator's thermal/flame-retardant properties. This work pioneers the multifunctional use of DOPO in lithium-ion battery separators, combining flame retardancy, enhanced Li + conductivity, and improved stability, offering a novel approach to producing safer, high-performance separators for large-scale applications. Advanced Science, Volume 13, Issue 2, 9 January 2026.