Microstructure engineering via one-step in-situ crosslinking co-carbonization for low-cost and high-performance hard carbon anodes in sodium-ion batteries

Sodium-ion batteries (SIBs) are regarded as a promising and cost-effective alternative to Lithium-ion batteries (LIBs) due to the abundance and low cost of sodium. However, graphite anodes cannot reversibly intercalate Na+, and most reported hard-carbon anodes still struggle to achieve a balanced performance portfolio—including high initial Coulombic efficiency (ICE), high specific capacity, superior rate capability, and long-term cycling stability. Herein, we present a simple and low-cost one-step co-carbonization strategy to precisely engineer the microstructure of hard carbon by using lignite as a precursor and glucose as a cross-linking agent. The resulting carbon exhibits expanded interlayer spacing, reduced surface defects, and optimized pseudo-graphitic domains, which collectively enable efficient and fast Na+ storage. The LG-55 delivers a high reversible capacity of 313.64 mA h g−1 with an ICE of 79.9% at 0.1 C, retains 87.3% of its capacity after 1000 cycles at 1 C, and demonstrates excellent rate performance. In situ X-ray diffraction and operando Raman spectroscopy consistently reveal a dual-mode “adsorption–intercalation” sodium-storage mechanism, with surface-dominated adsorption prevailing in the high-voltage slope region (>0.1 V) and interlayer intercalation dominating in the low-voltage plateau region (<0.1 V). This work offers a viable microstructural design strategy for advanced carbon materials in practical SIBs.