Engineering Se/N co-doped hard CNTs with localized electron configuration for superior potassium storage

The earth-abundant hard carbons have drawn great concentration as potassium-ion batteries (KIBs) anode materials because of their richer K-storage sites and wider interlayer distance versus graphite, but suffer from a low electrochemical reversibility. Herein, the novel Se/N co-doped hard-carbon nanotubes (h-CNTs) with localized electron configuration are demonstrated by creating unique N-Se-C covalent bonds stemmed from the precise doping of Se atoms into carbon edges and the subsequent bonding with pyrrole-N. The strong electron-donating ability of Se atoms on d-orbital provides abundant free electrons to effectively relieve charge polarization of pyrrole-N-C bonds, which contributes to balance the K-ion adsorption/desorption, therefore greatly boosting reversible K-ion storage capacity. After filtering into self-standing anodes with weights of 1.5–12.4 mg cm−2, all of them deliver a high reversible gravimetric capacity of 341 ± 4 mAh g−1 at 0.2 A g−1 and a linear increasing areal capacity to 4.06 mAh cm−2. The self-standing anode can still maintain 209 mAh g−1 at 8.0 A g−1 (93.3% retention) for a long period of 2000 cycles with a constant Se/N content. © 2022 Wiley-VCH GmbH.