Molecular secondary recombination for pitch-derived carbon microsphere toward ultra-high sodium storage

Abstract

Because the direct carbonization of low-cost pitch will form a highly graphitized soft carbon, and the soft carbon lacks a low-voltage platform to store sodium, so the sodium storage performance is poor. Therefore, in this research, by combining defect and pore engineering, the porous carbon microspheres with primary oxygen crosslinking were reorganized through secondary sulfur crosslinking to achieve the oxygen/sulfur complex crosslinked defect structure. At the same time, small molecular sulfur fragments filled the pores of the porous carbon microspheres to form the ultramicropores structure. It is worth noting that this pitch-derived carbon microsphere exhibits a new sodium storage mechanism of a new 'high-voltage platform'. Therefore, it shows stable cycle performance (220 mAh g−1 at 1 A g−1 after 2000 cycles) and excellent rate performance (101 mAh g−1 at 10 A g−1) in half cells; In addition, the structure of the ultramicropores can improve the initial coulomb efficiency of carbon microspheres. The sodium storage mechanism dominated by surface adsorption was determined by kinetic analysis and in-situ characterization techniques. This study provides a new idea for precise molecular regulation of anode materials for sodium ion batteries.