预氧化调控无烟煤衍生硬碳结构及其储钠性能OA

Anthracite is considered to be a promising precursor for hard carbon anodes in sodium-ion batteries(SIBs),primarily due to its naturally high fixed-carbon content,structural stability,and low cost.However,the direct carbonization of anthracite tends to induce excessive graphitization,which results in insufficient interlayer spacing(d002)and consequently leads to limited sodium-storage capacity.In particular,it diminishes the plateau capacity in the low-potential region that is critical for achieving high energy density in SIBs.To overcome these structural limitations,in this work we systematically investigated and compared multiple pre-oxidation strategies—including air oxidation,single-acid treatments,and mixed-acid oxidation—aimed at modifying the microstructure of anthracite before carbonization.We identified a mixed-acid oxidation method using sulfuric acid(H2SO4)and nitric acid(HNO3)as the most effective one.Under optimized conditions of 70℃for 9 hours,this method successfully modulates the graphite-like microdomains in the carbon precursor.In this process,sulfuric acid acts as a sulfonating and intercalating agent,introducing sulfonic groups(—SO3H)that help break the dense aromatic structure of anthracite and expand the interlayer spacing.Nitric acid serves as a strong oxidant,incorporating nitrogen-and oxygen-containing functional groups that promote cross-linking between aromatic layers,thereby suppressing graphitization during high-temperature treatment.The synergistic effect of both acids also facilitates the formation of abundant ultramicropores and closed pores.The optimized hard carbon material exhibits significantly improved electrochemical performance.It delivers a reversible capacity of 321.15 mAh/g at 0.02 A/g,with a plateau capacity of 210.7 mAh/g.Even at the high current density of 2.0 A/g,it maintains a capacity of 207.3 mAh/g,demonstrating excellent rate capability.To investigate the sodium-storage mechanism of the best-performing sample,we employed cyclic voltammetry and a galvanostatic intermittent-titration technique.The results suggest that the capacity in the low-potential region(0.01-0.1 V)arises mainly from sodium-ion insertion into the expanded interlayers and filling into closed pores,supporting a combined"adsorption-intercalation/filling"mechanism.In summary,this study demonstrates a rational and effective pre-oxidation strategy for achieving molecular-level structural tailoring of anthracite-derived hard carbon.The proposed mixed-acid treatment not only enhances the interlayer spacing and introduces beneficial functional groups but also creates a favorable pore structure for sodium storage.These findings offer valuable new insights into the design of low-cost,high-performance carbon anodes for SIBs and underscore the importance of precursor engineering in regulating sodium-storage behavior for next-generation energy-storage systems.