Small-molecule organic electrode materials for rechargeable batteries

Small-molecule organic electrode materials(SMOEMs)have shown tremendous potential as cathodes or anodes for various rechargeable batteries including lithium and sodium batteries,due to their easy material availability,high structure designability,attractive theoretical capacity,and wide adaptability to counterions.However,they suffer from the severe dissolution problem and the subsequent shuttle effect in nonaqueous electrolytes,which cause the poor cycling stability and Coulombic efficiency.To satisfy the demands on the energy density and cycling stability simultaneously,the molecular structures of SMOEMs need to be rationally designed,and extrinsic approaches including electrode engineering and electrolyte optimizations can be further conducted.In this review,we summarize the fundamental knowledge about SMOEMs,including their working principles and applications,structure classifications,molecular structure design methods,and extrinsic optimization strategies.Moreover,we also provide some original insights aiming at guiding the research and development of SMOEMs in a more scientific and practical way.In brief,SMOEMs are facing huge opportunities and challenges as candidates to enable the next-generation of efficient,sustainable,and green rechargeable batteries.

Covalent organic framework containing dual redox centers as an efficient anode in Li-ion batteries

Covalent organic frameworks(COFs)with periodic channels and tunable chemical structures have been widely considered as promising electrode materials in rechargeable batteries.However,the design and construction of high-performance COFs-based electrodes still face some challenges in the introduction of multiple efficient redox centers as well as the reduction of dead mass.To address these issues,a unique COF containing double active centers(C═N and N═N)is developed as an anode in rechargeable lithium-ion batteries(LIBs).The as-prepared COF displays excellent electrochemical performance due to its remarkable structural stability and the existence of many active groups.Meanwhile,its electrochemical performance is significantly better than that of the small molecule compound or the linear polymer with the same construction units.Even at a high current density of 5 A/g,the LIBs with COF electrodes remain at a high discharge capacity of 227 mAh/g after 2000 cycles.Moreover,the distinction in electrochemical performances of these three materials is further revealed by calculation.This study illustrates the importance of molecular structure design for improving the performance of organic electrodes.