Inhibition of lithium dendrite growth by high-thermal-stability separator containing sulfonated covalent organic frameworks and polybenzimidazole

Li-ion batteries (LIBs) are considered an excellent energy storage system because of their ultrahigh energy density. However, safety problems caused by the shrinkage of their separators at high temperatures and the growth of lithium dendrites have seriously limited their further development and application. Therefore, it is important to develop a separator with excellent heat resistance that inhibits the growth of lithium dendrites. In this work, bifunctional separators are prepared using poly(aryl ether benzimidazole) (OPBI) and sulfonated covalent organic frameworks (SCOFs). OPBI is used as the matrix material of the separator owing to its outstanding thermal properties, and the microstructure and polar functional groups of the SCOFs regulate the transport of Li+ and reduce the growth of lithium dendrites. The obtained SCOF15@OPBI hybrid separators exhibited excellent thermal stability (no change in physical size at 200 °C for 1 h) and stabilized the lithium plating/stripping process on the anode for more than 3200 h with a relatively low voltage hysteresis of roughly 1.6 mV at 0.5 mA cm−2. The hybrid separator also showed high ionic conductivity (1.76 mS cm−1) and an outstanding electrolyte uptake rate (439%), and a cell containing the hybrid separator exhibited a satisfactory discharge specific capacity (153.2 mA h g−1). The hybrid separator promotes large-scale energy storage applications of LIBs.