Enhancing the safety and cyclic performance of lithium-ion batteries using heat resistant and wettable separator based on covalent organic framework and polybenzimidazole

Abstract

The separator, an indispensable part of lithium-ion batteries (LIBs), plays a vital role related to the safety and electrochemical performance of these batteries because its thermal stability, mechanical properties, and ionic conductivity directly influence the performance and safety of LIBs. This work presents the preparation of a novel LIBs separator through the introduction of a covalent organic framework (COF) into poly(arylene ether benzimidazole) (OPBI). COFs are emerging crystalline porous organic polymers with large specific surface area and facile functionalization, which can promote electrolyte penetration. OPBI is a type of polymer known for its excellent thermal stability, inherent flame retardancy, and strong mechanical properties. Therefore, compared with the polypropylene separator, the obtained OPBI@COF separator presented an enhanced electrolyte uptake rate (428%), higher ionic conductivity (1.214 mS cm−1), excellent thermal stability, and first-rate flame retardancy. The specific discharge capacity of LiFePO4/Li cell assembled with the OPBI@COF20 separator is 148.3 mAh g−1, and the cell capacity retention reached 98.98% after 200 cycles at 0.5C. More interestingly, the OPBI@COF separator enhanced the safety of LIBs, even after a long run time, by suppressing lithium dendrite growth. Thus, OPBI@COF separator can be considered as an effective and highly stable LIB separator.