Porous carbon microspheres assembled by defective nitrogen and sulfur co-doped nanosheets as anode materials for lithium-/sodium-ion batteries

Carbon-based anode materials are widely used in various battery energy storage systems due to their low cost, wide source, high conductivity and easy morphology control. However, current commercially available anode materials as active materials for lithium-/sodium-ion batteries generally suffer from large volume changes and poor rate performance. In response, we synthesized defect-rich N, S co-doped two dimensional (2D) nanosheet-assembled porous carbon microspheres (N, S-PCS) via simple hydrothermal, carbonization and etching process based on the principle of Schiff base reaction. The N, S-PCS structure is thus constructed by removing Fe₇S₈ nanoparticles from the carbon skeleton to form porous microspheres with N, S doping. Therefore, the micromorphology characteristic, pore structure and electro-conductivity of carbon materials are effectively optimized via heteroatom doping and surface engineering. As expected, the prepared N, S-PCS electrodes exhibit excellent electrochemical performance in both lithium-ion and sodium-ion batteries. For lithium-ion batteries, it achieves reversible capacities of 1045 and 237 mAh g⁻¹ at 0.1 and 20 A g⁻¹, respectively. For sodium-ion batteries, it shows good cycling stability with a capacity of 157 mAh g⁻¹ after 500 cycles at 1 A g⁻¹. Experimental and theoretical calculation results confirm that the N, S co-doping strategies help to improve the structural stability, shorten the ion diffusion paths, and promote the reaction kinetics, thus achieving excellent electrochemical performance. This work is instructive for the practical application of nonmetal doping functionalized porous carbon structures for metal-ion batteries.