Heteroatom dopant strategy triggered high-potential plateau to non-graphitized carbon with highly disordered microstructure for high-performance sodium ion storage

Non-graphitized carbon (NGC) has been extensively utilized as carbonaceous anode in sodium-ion batteries (SIBs). However, more optimization to achieve competitive capacity and stability is still challenging for SIBs. In the study, the dopant strategy is utilized to construct nitrogen/sulfur-doped non-graphitized carbon (N-NGC or S-NGC) shell decorated on three-dimensional graphene foam (GF) as a self-support electrode. The highly disordered microstructures of heteroatom doped carbons are produced by applying a low-temperature pyrolysis treatment to precursors containing nitrogen and sulfur. The DFT calculations of Na-ion adsorption energies at diverse heteroatom sites show marginal-S, pyrrolic N and pyridinic N with more intensive Na-ion adsorption ability than middle-S, CO and pristine carbon. The N-NGC with dominant small graphitic regions delivers adsorption ability to Na-ion, while the S-NGC with significant single carbon lattice stripes demonstrates redox reaction with Na-ion. Evidently, in comparison with only adsorption-driven slope regions at high potential for N-NGC, the redox reaction-generated potential-plateau enables non-graphitized S-NGC superior discharge/charge capacity and cycle-stability in the slope region. This work could provide deep insight into the rational design of non-graphitized carbon with rich microstructure and composition.