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

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.