Hard Carbon Microsphere with Built-In Electron Transport Channels as a High-Performance Anode for Sodium-Ion Batteries

Hard carbon is one of the most promising candidate materials as the anode for sodium-ion batteries (SIBs). In this work, we developed an effective strategy to homogenize highly conductive carbon nanotubes (CNTs) into a hard carbon microsphere (e-HC) to construct electron transport channels to improve the performance of hard carbon. The material featured a wrinkled hard carbon microsphere with built-in electron transport channels. Although the optimization made no significant changes in the particle size and the graphitization state for the hard carbon, the electrochemical performance was greatly improved in comparison with the pure hard carbon material without CNTs (HC). The increase in the electric and ionic conductivity was identified. The electrochemical measurements showed that the e-HC electrode delivered a reversible capacity of 335.6 mAh g(-1) at 0.05 mA g(-1), which was higher than that of the HC electrode (304.1 mAh g(-1) at 0.05 mA g(-1)). The as-synthesized e-HC material exhibited a higher rate performance and a better cycle life than the HC material. The correlated mechanism for the enhancement was proposed in this study. The e-HC material can be used as a feasible anode for SIBs.