In-situ ScOOH coaxially armored polyimide nanofibrous separator with high electrolyte wettability and thermostability for high-safety and high-rate capability lithium-ion batteries

With the growing demand for electric vehicles and grid-scale energy storage, conventional polyolefin separators fall short in meeting the thermal and electrochemical requirements of next-generation lithium-ion batteries (LIBs). Herein, a polyimide-based composite separator (PI@ScOOH) was developed via alkali-etching, adsorption–complexation, and hydrolysis to in situ coat scandium oxyhydroxide (ScOOH) onto a PI nanofiber matrix. The ScOOH coating introduced physical crosslinking among fibers, significantly enhancing mechanical integrity. Compared to polyolefin separators, PI@ScOOH exhibited superior electrolyte wettability (contact angle: 9.05° vs 48.53°) and thermal dimensional stability (TMA onset: 350 °C vs 140 °C). Flame retardancy tests confirmed its excellent safety characteristics. Electrochemical evaluation using NCM811/Li full cells showed that the PI@ScOOH separator achieved higher capacity retention (96.7 % vs 90.9 % after 300 cycles at 1C) and enhanced rate capability (142.8 mAh·g⁻¹ vs 106.9 mAh·g⁻¹ at 10C) relative to polyolefin counterparts. Notably, the separator maintained operational stability at 120 °C for 90 min, far exceeding the 10-min limit of conventional separators. These results indicate that PI@ScOOH is a new type of lithium-ion battery separator with enhanced safety and electrochemical properties.