Sulfur and Nitrogen Codoped Hard Carbon with Expanded Interlayer Distance as an Effective Anode Material for Sodium-Ion Batteries

Development of sodium-ion battery (SIB) anodes using cost-effective and earth-abundant elements has gained a lot of attention nowadays. The most promising SIB anode materials still involve carbon-based materials. The graphite-based materials used in lithium-ion batteries do not work well for SIB anodes as they have insufficient interlayer spacing. Crystallinity, doping functionality, and morphology tuning are, therefore, crucial to enhance the anodic performance of carbonaceous materials for SIBs. Herein, sulfur and nitrogen codoped hard carbon (SNHC-X) was prepared as an effective anode material for SIBs. The dual doping of sulfur and nitrogen in carbon increases the interlayer spacing, defects, and electrical conductivity of SNHC-X, which facilitates the Na + adsorption capacity, charge diffusion, and mass transportability. The optimized SNHC-1400 electrode exhibits ∼268 mA h/g specific capacity at 25 mA/g current density with 77.4% initial Coulombic efficiency. The composite also possesses good cyclic stability at 100 mA/g current density with ∼86.5% capacity retention after 100 cycles. Furthermore, electrochemical impedance spectroscopy of SNHC-1400 shows the promoted Na + diffusion dynamics between the interlayers of microcrystalline structures, thereby boosting Na + insertion through a diffusion-controlled process. Moreover, the assembled full-cell (SNHC-1400 ∥ NVP) displays excellent cycling stability and 231 mA h/g specific capacity at 25 mA/g from the anode side. Thus, sulfur and nitrogen codoping into the carbon material may offer a promising prospect for developing sodium-ion storage anodes.