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

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.