Yolk‐Shell Spindle‐Shaped FeSe2@N‐Doped Carbon Decorated on rGO with High‐Rate Capability and Cycling Stability in a Wide Temperature Range for Sodium Ion Batteries**

Abstract Iron selenides (FeSe 2 ) have been utilized in sodium ion batteries due to abundant reserves of elements and ideal specific capacities. However, they suffer from volume expansion and low electrical conductivity, limiting their application. In this study, multiple strategies including fabrication of hollow FeSe 2 nanospindles and N‐doping carbon (NC) coating, accompanied by the introduction of highly conductive and flexible reduced graphene oxide (rGO) were adopted to construct a yolk‐shell spindle‐shaped FeSe 2 @NC with rGO composite, abbreviated as YS‐FeSe 2 @NC@rGO, in which the hollow structure can provide more space for volume expansion to guarantee the structural stability and the coating of double‐layer carbon is favorable to accelerate reaction kinetics, stabilizing the solid electrolyte interfaces (SEI) film. Accordingly, the YS‐FeSe 2 @NC@rGO electrode for sodium ion battery shows capacity of 639.1 mAh g −1 (565.6 mAh cm −2 ) after 100 cycles at 0.1 A g −1 . Even at a high current density of 10 A g −1 , the specific capacity after 880 cycles is 320.7 mAh g −1 (283.9 mAh cm −2 ). Moreover, the YS‐FeSe 2 @NC@rGO composite holds high Na + diffusion coefficients ( D Na + , 1.17×10 −12 –2.617×10 −11 cm −2 s −1 ). The YS‐FeSe 2 @NC@rGO//NVP/C full cell also maintains a discharge capacity of 252.6 mAh g −1 after 135 cycles. Furthermore, the YS‐FeSe 2 @NC@rGO composite anode is capable of retaining high‐rate capability and capacity retention in a wide temperature range. Therefore, the excellent sodium storage performance makes the YS‐FeSe 2 @NC@rGO composite a desirable anode material for sodium ion batteries.