Hollow CoSe2-ZnSe microspheres inserted in reduced graphene oxide serving as advanced anodes for sodium ion batteries.

[Display omitted] • A new CoSe 2 -ZnSe@rGO composite with heterointerfaces is designed and synthesized. • The CoSe 2 -ZnSe@rGO composite behaves special structure characteristics. • The built-in electric field in the heterointerfaces is favorable for Na+ transfer. • The rGO could improve conductivity and alleviate volume variations of the active materials. • The CoSe 2 -ZnSe@rGO exhibits an enhanced coulombic efficiency and cycling stability. Transition metal selenides are promising anode candidates for sodium ion batteries (SIBs) because of their higher theoretical capacity and conductivity than metal oxides. However, the disadvantages of severe capacity degradation and poor magnification performance greatly limit their commercial applications. Herein, we have developed a new hollow bimetallic selenides (CoSe 2 -ZnSe)@reduced graphene oxide (rGO) composite with abundant heterointerfaces. The rGO could not only alleviate the volume variations of hollow CoSe 2 -ZnSe microspheres during cycling, but also improve the conductivity of composite. The presence of the heterointerfaces could help to accelerate ionic diffusion kinetics and improve electron transfer, resulting in the improved sodium storage performance. As an advanced anode for SIBs, the CoSe 2 -ZnSe@rGO exhibits an enhanced initial coulombic efficiency of 75.1% (65.2% of CoSe 2 @rGO), extraordinary rate capability, and outstanding cycling stability (540.3 mAh/g at 0.2 A/g after 150 cycles, and 395.2 mAh/g at 1 A/g after 600 cycles). The electrochemical mechanism was also studied by kinetic analysis, showing that the charging/discharging process of CoSe 2 -ZnSe@rGO is mostly related to a capacitive-controlled behavior. [ABSTRACT FROM AUTHOR]