Synthesis of Porous Ni‐Doped CoSe 2 /C Nanospheres towards High‐Rate and Long‐Term Sodium‐Ion Half/Full Batteries

Carbon‐layer‐coated porous Ni‐doped CoSe 2 (Ni‐CoSe 2 /C) nanospheres have been fabricated by a facile hydrothermal method followed by a new selenization strategy. The porous structure of Ni‐CoSe 2 /C is formed by the aggregation of many small particles (20–40 nm), which are not tightly packed together, but are interspersed with gaps. Moreover, the surfaces of these small particles are covered with a thin carbon layer. Ni‐CoSe 2 /C delivers superior rate performance (314.0 mA h g −1 at 20 A g −1 ), ultra‐long cycle life (316.1 mA h g −1 at 10 A g −1 after 8000 cycles), and excellent full‐cell performance (208.3 mA h g −1 at 0.5 A g −1 after 70 cycles) when used as an anode material for half/full sodium‐ion batteries. The Na storage mechanism and kinetics have been confirmed by ex situ X‐ray diffraction analysis, assessment of capacitance performance, and a galvanostatic intermittent titration technique (GITT). GITT shows that Na + diffusion in the electrode material is a dynamic change process, which is associated with a phase transition during charge and discharge. The excellent electrochemical performance suggests that the porous Ni‐CoSe 2 /C nanospheres have great potential to serve as an electrode material for sodium‐ion batteries.