Nanoconfined Strategy Optimizing Hard Carbon for Robust Sodium Storage

Developing non-graphitic carbons with unique microstructure is a popular strategy to enhance the significant potential in practical applications of sodium-ion batteries (SIB), while the electrochemical performance imbalances arising from their intricate active surface and porous structure pose significant challenges to its commercialization. Inspired by the structure of biological cell membranes, N/P co-doped hard carbon nanospheres (NPCS) anodes with abundant ultramicropores (≈0.6 nm) are proposed and synthesized as robust sodium anodes. Based on density functional theory calculations, optimizing ultramicropores can enable small Na⁺ to be well confined within the pores and hinder large solvent molecules from invading and reacting, introducing N/P species contributes to the rapid adsorption/diffusion of Na⁺. In situ XRD and Raman analysis suggest that the nanoconfinement strategy induced by abundant ultramicropores and N/P co-doping enables highly reversible electrochemical reactions. Electrochemical test confirms that the nanoconfinement strategy endows the NPCS anode with high reversible capacity (376.3 mAh g⁻¹ at 0.1 A g⁻¹), superior initial coulombic efficiency (87.3% at 1.0 A g⁻¹), remarkable rate capability (155.6 mAh g⁻¹ at 50.0 A g⁻¹) and excellent cycling stability (with capacity retention of ≈94.6% after 10 000 cycles), lightening a promising avenue for developing SIB with robust durability.