Sandwich-structured dual carbon modified bismuth nanosphere composites as long-cycle and high-rate anode materials for sodium-ion batteries

Abstract Bismuth as alloy-based anode material has a high theoretical specific capacity (385 mAh g−1) and volumetric capacity (3800 mAh cm−3). However, its severe volume expansion during the alloying process will cause structural collapse and capacity degradation. In this work, dual carbon materials containing outmost thin carbon layer and graphene are employed to modify bismuth nanospheres to form a sandwich-like carbon/bismuth/reduced graphene oxide composite (CPVP+C2H2/Bi/rGO), which is fabricated via a facile solvothermal method and subsequent chemical vapor deposition (CVD) strategy. The thin carbon layer coated on the surface of Bi nanoparticles can effectively suppress the huge volume changes of Bi. The graphene oxide as a conductive matrix favors the successful loading of Bi nanospheres, which limits the particle aggregation of Bi upon cycling. The dual carbon also can improve the conductivity of the overall electrode. As anode materials for sodium-ion batteries, the CPVP+C2H2/Bi/rGO shows excellent sodium storage performance, better than CPVP/Bi/rGO. At a high current density of 5 A g−1, this electrode can retain a capacity of up to 327.6 mAh g−1 after 1200 cycles. The assembled full battery with CPVP+C2H2/Bi/rGO as anode and Na3V2(PO4)3/rGO as cathode also presents good electrochemical performance. The outstanding electrochemical performance of CPVP+C2H2/Bi/rGO is attributed to the well-designed sandwich-like composite structure and synergistic effect of dual carbon and Bi nanospheres.