Sponge-like Nanoporous\nSiO<sub>2</sub>‑Based\nPolyethylene Separators for Safe Fast-Charging Lithium-Ion Batteries

Fast charging of lithium-ion batteries\n(LIBs) is currently\ncrucial\nfor the widespread use of electric vehicles and consumer electronics,\nbut this process is challenged by the rapid consumption of liquid\nelectrolytes. Commercial Al<sub>2</sub>O<sub>3</sub> ceramic-based\nseparators show low electrolyte absorption, so they cannot meet the\nfuture demands of fast charging. In this study, a sponge-like membrane\ncomposed of nanoporous SiO<sub>2</sub> and a polyethylene substrate\nwas developed as a separator for LIBs. The as-prepared SiO<sub>2</sub>-coated separator (S-CS) exhibits an excellent performance, including\na high swelling degree (362%), ionic conductivity (7.8 × 10<sup>–3</sup> S/cm at 25 °C), and a wide electrochemical stabilization\nwindow (5.1 V). The NMC523/S-CS/graphite pouch cell exhibits a discharge\ncapacity retention of 88.9% and a Coulombic efficiency of 99.7% over\n500 cycles at a fast-charging rate of 2 C and 25 °C. Furthermore,\nthe cell does not show any lithium plating and a lower surface temperature\n(33.6 °C) after cycling, which significantly improves the safety\nof the fast charging of LIBs. Therefore, this study offers useful\ninsights into the effect of separators on fast charging and strategic\nsuggestions for the safe fast-charging of LIBs.