Effect of Coating Asphalt Softening Point on Pre-Oxidation Pathway and Sodium Storage Performance of Derived Hard Carbon

• • Low (80 °C) and high (260 °C) softening point asphalts achieve high oxygen incorporation (20–25%) during pre-oxidation, forming deep cross-linking that suppresses graphitization, yielding hard carbon with large interlayer spacing and abundant closed pores, resulting in initial charge capacities of 314.7 and 306.6 mA·h/g, respectively. • • Medium softening point (160 °C) asphalt exhibits insufficient cross-linking with only ~5% oxygen content, leading to a dense structure with smaller interlayer spacing (3.46 Å) and a significantly reduced capacity of 173.2 mA·h/g, highlighting the nonlinear effect of softening point. • • First-cycle coulombic efficiencies of 81.3% (EPOC-80) and 79.3% (EPOC-260) demonstrate that optimized pre-oxidation pathways enhance reversible sodium storage, critical for practical anode efficiency. • • Both EPOC-80 and EPOC-260 show excellent cycling stability with capacity retention >81% after 100 cycles, indicating robust structural integrity for long-term battery operation.