Unlocking concurrent high initial coulombic efficiency and rate capability in hard carbon anodes via melamine-mediated pore and surface engineering

Hard carbon (HC) has emerged as the most widely adopted anode material for sodium-ion batteries (SIBs) owing to its low cost and controllable microstructure. Nevertheless, the practical application of HC is still hindered by the intrinsic trade-off between high initial Coulombic efficiency (ICE) and excellent rate capability. Herein, a straightforward melamine-assisted pore-structure reconfiguration strategy is developed to synergistically optimize the microstructure and surface chemistry of HC. The melamine-mediated reconstruction converts HC into a low-specific-surface-area hierarchical porous architecture while optimizing oxygen-containing functional groups on the surface, which collectively suppresses irreversible sodium consumption and accelerates Na + transport, thereby simultaneously improving ICE and rate capability. Consequently, the modified HC (MG-N-2) delivers a high reversible capacity of 346.2 mAh g −1 at 0.05 C with an ICE of 85.55%, and maintains a reversible capacity of 259.2 mAh g −1 even at 3.0 C. This work presents a straightforward strategy to alleviate the trade-off between ICE and rate capability, offering new insights for the design of high-performance HC anodes.