Two-Dimensional Covalent Organic Framework with Synergistic Active Centers for Efficient Electrochemical Sodium Storage

Abstract

Benefiting from the adjustable molecule structures, abundant functional units, large specific surface areas, and ordered pores, covalent organic frameworks (COFs) are highly desirable for electrochemical energy storage. Herein, a two-dimensional COF (denoted as HHTP-TABQ) with a fully π-conjugated framework and C═N and C═O dual-active sites has been synthesized and applied as the anode in organic rechargeable sodium-ion batteries (SIBs). During the sodium-storage process, it delivered remarkable rate capability, satisfactory ultra-long cycle stability (84.5% capacity retention ratio after 1000 cycles at 5000 mA g-1), and facile charge exchange kinetics (2.49 × 10-7 cm2 s-1), which is superior among most reported COF-based electrodes. Furthermore, the sodiation mechanism was investigated by density functional theory calculations and ex situ characterizations, which confirms that the electrochemical reaction is dominated by the synergistic reaction of C═N and C═O groups. These results suggest that COFs with stable π-conjugated structures, insoluble characteristics, and abundant active sites would have great potential for practical applications in rechargeable SIBs.