Fabrication of pitch-derived hard carbon via bromination-assisted pyrolysis strategy for sodium-ion batteries

Abstract

Pitch-derived hard carbon materials have been regarded as one of the most promising anodes for sodium-ion batteries (SIBs) due to their low cost and high carbon yields, but are largely limited by the inferior specific capacity and rate capability, resulting from the easy graphitization property of the pitch precursor during high-temperature carbonization. Herein, a simple bromination modification coupled with a pyrolysis strategy was proposed to fabricate the pitch-derived hard carbon anode (BHC-x), aiming to engineer its microstructure and further optimize the electrochemical performance of SIBs. The detailed experimental investigations demonstrated that the brominated pitch precursor obtained by a hydrothermal treatment tends to occur the cross-linking polycondensation in the presence of bromine species at 350 oC, thereby forming hard carbon with unique disordered and closed structure during the high-temperature pyrolysis process. As a result, the optimized BHC-1500 with rich defect sites and suitable interlayer space of 0.358 nm exhibits a high reversible capacity of 250.0 mAh g‒1 at 0.1 A g‒1 with an initial coulombic efficiency (ICE) of 79.8% and it still maintains 150 mAh g‒1 at 5 A g‒1, outperforming unbrominated counterparts (152.1 mAh g‒1 at 0.1 A g‒1). This work proposes a new insight into the optimization of pitch-based hard carbon anode for high-performance SIBs.