Nitrogen and sulfur co-doped graphene nanoribbons with well-ordered stepped edges for high-performance potassium-ion battery anodes

Graphitic carbon materials, particularly few-layered graphene, exhibit great potentials as potassium-ion battery (PIBs) anodes. However, bulk graphene-based materials have the disordered structure owing to randomly stacked graphene layers, which causes the high migration barrier during K+ intercalation/deintercalation reactions and thus the surface-dominated capacitive response. Here, we present a novel nanoarchitecture of nitrogen and sulfur co-doped graphene nanoribbons with well-ordered stepped edges (NS–sGNR) via the electrochemical unzipping of multiwalled carbon nanotubes (MWCNTs) and the subsequent N/S co-doping process for high-performance PIB anodes. As an anode material for PIBs, the prepared sample exhibits high initial capacity (329.1 mAh g−1 at 50 mA g−1), superior rate capability (211.7 mAh g−1 at high current density, 2000 mA g−1), outstanding reversibility of K-staging, and stable long-term cyclability. Theoretical calculations were conducted to demonstrate that sGNRs with NS co-doping (NS–sGNR) exhibit much improved K+ intercalation properties, such as the K+ adsorption energy, charge transfer, and migration barriers, compared with the parallel-edged GNRs. Particularly, the migration barrier (the rate-determining step) can be substantially reduced at the stepped edges during K+ intercalation.