Small amount COFs enhancing storage of large anions

Abstract Various alternatives of Li-ion batteries (LIBs) have been developed due to the scarcity of Li resources and growing demand of LIBs. However, most of these candidates are suffering the challenges of sluggish intercalations of large-sized ions (e.g. Na+, K+ or anions etc.), leading to low capacity, poor cycleability and particularly performance decay at high rate. Herein, we report the precise synthesis of a novel conjugated polymer (polypyrene sulfide, PPYS) and its application in storage of anions. Furthermore, we propose a novel concept that the electropositive covalent organic frameworks (COFs) could be able to adsorb anions by electrostatic attractions and thereby facilitate the transport of anions. This novel concept for enhancing the intercalation kinetics of large-sized anions is demonstrated by using the PPYS cathodes as proof-of-concept. After addition of small amount COFs, the capacity, the rate capability and the cycleability of PPYS are improved impressively. Such strategy can be expected to be universal to other redox polymers and may be also applicable to enhance the transport of other large-sized ions in multifunctional applications. These results will also extend the application fields of COFs.