Biochemical fulvic acid derived amorphous carbon modified microcrystalline graphite as low-cost anode for potassium-ion storage

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.

Nitrogen-Doped Porous Carbon Derived from Coal for High-Performance Dual-Carbon Lithium-Ion Capacitors

Lithium-ion capacitors (LICs) are emerging as one of the most advanced hybrid energy storage devices, however, their development is limited by the imbalance of the dynamics and capacity between the anode and cathode electrodes. Herein, anthracite was proposed as the raw material to prepare coal-based, nitrogen-doped porous carbon materials (CNPCs), together with being employed as a cathode and anode used for dual-carbon lithium-ion capacitors (DC-LICs). The prepared CNPCs exhibited a folded carbon nanosheet structure and the pores could be well regulated by changing the additional amount of g-C3N4, showing a high conductivity, abundant heteroatoms, and a large specific surface area. As expected, the optimized CNPCs (CTK-1.0) delivered a superior lithium storage capacity, which exhibited a high specific capacity of 750 mAh g-1 and maintained an excellent capacity retention rate of 97% after 800 cycles. Furthermore, DC-LICs (CTK-1.0//CTK-1.0) were assembled using the CTK-1.0 as both cathode and anode electrodes to match well in terms of internal kinetics and capacity simultaneously, which displayed a maximum energy density of 137.6 Wh kg-1 and a protracted lifetime of 3000 cycles. This work demonstrates the great potential of coal-based carbon materials for electrochemical energy storage devices and also provides a new way for the high value-added utilization of coal materials.