A review of covalent organic framework electrode materials for rechargeable metal-ion batteries

Covalent organic frameworks (COFs) are highly promising electrode materials for next-generation rechargeable metal-ion batteries owing to their robust framework, abundant electrochemically active sites, well-defined and tunable pores and channels for metal ion transfer, and adjustable molecular structures for improving electrochemical performance. Moreover, COFs do not have the problems caused by expensive or toxic elements in conventional inorganic electrode materials or the cycling stability challenges existing in small organic molecules, and thus have great potential as electrode materials in next-generation rechargeable metal-ion batteries. We summarize the electrochemically active sites of these materials for charge storage, and most importantly, we focus on strategies for improving their electrochemical performance, including energy density, rate performance and cycling life by changing their frameworks, pores, active sites, and electronic structures. To fabricate high performance COF electrodes, much more effort is needed to improve their ionic and electronic conductivities, increase their operating voltage, and reveal their mechanisms of energy storage. This review may shed light on developing high performance COF electrode materials for next-generation rechargeable metal-ion batteries.