Biomass-derived carbon-sulfur hybrids boosting electrochemical kinetics to achieve high potassium storage performance

Potassium-ion batteries (PIBs) as an emerging battery technology have garnered significant research interest. However, the development of high-performance PIBs critically hinges on reliable anode materials with comprehensive electrochemical performance and low cost. Herein, low-cost N-doped biomass-derived carbon-sulfur hybrids (NBCSHs) were prepared through a simple co-carbonization of the mixture of a biomass precursor (coffee grounds) and sulfur powder. The sulfur in NBCSHs predominantly exists in the form of single-atomic sulfur bonded with carbon atoms (CSC), functioning as main active redox sites to achieve high reversible capacity. Electrochemical evaluations reveal that the NBCSH 1–3 with moderate sulfur content shows significantly improved potassium storage performance, such as a high reversible capacity of 484.7 mAh g−1 and rate performance of 119.4 mAh g−1 at 5 A g−1, 4.5 and 14.7 times higher than that of S-free biomass-derived carbon, respectively. Furthermore, NBCSH 1–3 exhibits stable cyclability (no obvious capacity fading even after 1000 cycles at 0.5 A g−1) and excellent electrochemical kinetics (low overpotentials and apparent diffusion coefficients). The improved performance of NBCSHs is primarily attributed to pseudocapacitance-dominated behavior with fast charge transfer capability. Density functional theory calculations also reveal that co-doping with S, N favors for achieving a stronger potassium adsorbing capability. Assemble K-ion capacitors with NBCS 1–3 as anodes demonstrate stable cyclability and commendable rate performance. Our research envisions the potential of NBCSHs as efficient and sustainable materials for advanced potassium-ion energy storage systems.