Dynamic control of crystallization rate enables efficient sodium storage in coal-based hard carbon: synergistic effects of short-range ordered structure and closed pores

Abstract

Coal-derived hard carbon (HC) represents a promising anode material for sodium-ion batteries owing to its cost-effectiveness and high carbon yield. However, conventional carbonization induces excessive graphitization, yielding insufficient interlayer spacing (d₀₀₂ < 0.37 nm) and underdeveloped closed pores. Herein, we propose a dynamic crystallization control strategy through carbothermal shock treatment (1300 °C, 30 s) that decouples thermodynamic and kinetic constraints. This method precisely modulates graphite domain ordering kinetics, producing short-range ordered structures with expanded interlayer spacing (d₀₀₂ = 0.385 nm) and homogeneously distributed closed nanopores. Through combined in situ characterization and first-principles calculations, we elucidate a three-stage crystallization mechanism: (i) amorphous carbon transformation, (ii) open-pore collapse, and (iii) pseudo-graphitic ordering. The optimized HC achieves record performance with 88.6 % initial Coulombic efficiency and 204 mA h g⁻¹ plateau capacity, while its optimal interlayer spacing lowers Na⁺ diffusion barriers to enable exceptional rate capability (221 mA h g⁻¹ at 0.5C after 300 cycles). Practical pouch cells maintain 85 % capacity retention after 100 cycles at −20 °C and deliver 284 Wh kg⁻¹ energy density. This work establishes a kinetic regulation paradigm for graphitization-prone precursors, advancing the rational design of high-performance HC anodes.