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

• C PVP+C2H2 /Bi/rGO is fabricated by a solvothermal and subsequent chemical vapor deposition strategy. • The dual carbon can improve the conductivity and suppress the huge volume changes of Bi. • The C PVP+C2H2 /Bi/rGO exhibits excellent cycling performance and rate capability for Na-ion batteries. • The electrochemical performance of C PVP+C2H2 /Bi/rGO is better than C PVP /Bi/rGO. • The assembled full battery with C PVP+C2H2 /Bi/rGO as anode presents good electrochemical performance. 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 (C PVP+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 C PVP+C2H2 /Bi/rGO shows excellent sodium storage performance, better than C PVP /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 C PVP+C2H2 /Bi/rGO as anode and Na 3 V 2 (PO 4) 3 /rGO as cathode also presents good electrochemical performance. The outstanding electrochemical performance of C PVP+C2H2 /Bi/rGO is attributed to the well-designed sandwich-like composite structure and synergistic effect of dual carbon and Bi nanospheres. Image, graphical abstract [ABSTRACT FROM AUTHOR]