High-Performance Sodium-Ion Battery Cathode in Three-Dimensional Covalent Organic Frameworks with Interconnected Microchannels and Dense Redox-Active Sites

Covalent organic frameworks (COFs) have increasingly attracted attention as renewable cathode materials for sodium-ion batteries (SIBs). However, the two-dimensional COF cathodes employed thus far for storing Na + ions still exhibit unsatisfactory energy and power densities due to their insufficient active-site utilization and sluggish redox kinetics. Herein, two new three-dimensional (3D) COFs (named 3D-TP-HATN-COF and 3D-TAM-HATNCOF) with multiple bipolar redox-active sites for SIBs were fabricated from reacting triphenylene2,3,6,7,10,11-hexacarboxylic acid with N , N , N ' , N '- tetraphenyl-1,4-phenylenediamine and tetrakis (4-aminophenyl)methane, respectively. These two 3D COFs possess ctn topology with interconnected channels composed of micropores of 1.3 and 1.5 nm, according to powder X-ray diffraction in conjunction with theoretical simulation and N 2 sorption measurement. These structural merits facilitate the rapid transport of Na + and PF 6 - with high ion diffusion of 7.4 x 10 -9 and 4.5 x 10 -9 cm 2 s -1 for 3D-TP-HATN-COF and 3D-TAM-HATN-COF, respectively. This, in combination with the abundant and fully exposed p-type and n-type redox-active sites as well as robust skeleton of 3D-TP-HATN-COF, results in the remarkable energy density of 445 W h kg -1 and a power density of 21,360 W kg -1 at a high current density of 10 A g -1 , representing one of the best performances among the reported SIB electrodes.