Heterogeneous carbon coated resin-based hard carbon anode material for high-performance sodium ion batteries

Abstract

Resin-based hard carbons are promising anode materials for sodium ion batteries (SIBs) due to their high storage capacity and purity. However, the low initial coulombic efficiency (ICE) still hinders their practical application. Crosslinking and high-temperature pyrolysis strategies have been demonstrated to improve ICE effectively, but the complex process and high energy consumption hinder their industrialization. This paper proposes a facile synthesis of resin-based hard carbon with a soft carbon coating strategy to improve ICE. By carbonizing commercial phenolic resin at 1150℃, hard carbon with a reversible capacity of 291.6 mAh g−1 and 82.6 % ICE was obtained. After asphalt-based soft carbon coating, the optimized sample (CHC-1150) with a heterogeneous carbon coating layer of about 8.5 nm displays a high reversible capacity and ICE of 309.8 mAh g−1 and 88.2 %. Moreover, when combined with NaFe1/3Ni1/3Mn1/3O2 cathode, the assembled 18650 cylindrical-type batteries deliver a high ICE of 84.3 %, excellent low-temperature capability and cycling stability. Additionally, the disassembly results after cycling indicate that the soft carbon layer can inhibit the decomposition of electrolytes and avoid sodium plating. These encouraging results suggest that heterogeneous carbon coating should be a promising strategy to promote the electrochemical performance of resin-based hard carbon anode materials for SIBs.