Sponge-like Nanoporous SiO₂-Based Polyethylene Separators for Safe Fast-Charging Lithium-Ion Batteries

Fast charging of lithium-ion batteries (LIBs) is currently crucial for the widespread use of electric vehicles and consumer electronics, but this process is challenged by the rapid consumption of liquid electrolytes. Commercial Al₂O₃ ceramic-based separators show low electrolyte absorption, so they cannot meet the future demands of fast charging. In this study, a sponge-like membrane composed of nanoporous SiO₂ and a polyethylene substrate was developed as a separator for LIBs. The as-prepared SiO₂-coated separator (S-CS) exhibits an excellent performance, including a high swelling degree (362%), ionic conductivity (7.8 × 10^-3 S/cm at 25 °C), and a wide electrochemical stabilization window (5.1 V). The NMC523/S-CS/graphite pouch cell exhibits a discharge capacity retention of 88.9% and a Coulombic efficiency of 99.7% over 500 cycles at a fast-charging rate of 2 C and 25 °C. Furthermore, the cell does not show any lithium plating and a lower surface temperature (33.6 °C) after cycling, which significantly improves the safety of the fast charging of LIBs. Therefore, this study offers useful insights into the effect of separators on fast charging and strategic suggestions for the safe fast-charging of LIBs.