Dual Carbon Source Synergistic Carbonization Strategy to Enhance the Sodium Storage Performance of Coal-Based Hard Carbon for Sodium-Ion Batteries

Coal-based hard carbon is regarded as the most commercially promising anode material for sodium-ion batteries (SIBs) due to its abundant production and ultrahigh carbonization yield. However, due to the stacking and rearrangement of carbon layers during high-temperature carbonization, coal-based hard carbon has a high degree of graphitization, which seriously limits its sodium storage capacity. Therefore, we adopted a carbon–carbon composite carbonization method, using carbohydrates (glucose, starch, and sucrose) mixed with bituminous coal for carbonization. The rich oxygen functional groups in carbohydrates undergo strong cross-linking reactions with bituminous coal during high-temperature carbonization, inhibiting the graphitization process of carbon layers and achieving a synergistic optimization effect through mixed carbonization. The prepared composite hard carbon exhibits more excellent sodium storage performance. Additionally, the optimal addition ratios of bituminous coal mixed with three carbohydrates for carbonization were explored, and the reasons for the performance differences were revealed from the perspective of carbonization behavior. Benefiting from the rational regulation of graphitization degree, when glucose is used as the carbon source, the sodium storage capacity of BC-Glu-73 significantly increases from 253.6 to 297.2 mAh g–1, with an initial Coulombic efficiency (ICE) as high as 82.7%, and it shows the most excellent sodium storage kinetics in all samples. Finally, the optimal addition amounts of glucose, starch, and sucrose were determined to be 30, 50, and 70%, respectively. The collaborative carbonization strategy adopted in this study offers a possible path for the development of advanced coal-based anode materials suitable for commercial sodium-ion batteries.