Synthesis of Porous Ni-Doped CoSe2 /C Nanospheres towards High-Rate and Long-Term Sodium-Ion Half/Full Batteries.

Carbon-layer-coated porous Ni-doped CoSe2 (Ni-CoSe2 /C) nanospheres have been fabricated by a facile hydrothermal method followed by a new selenization strategy. The porous structure of Ni-CoSe2 /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-CoSe2 /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-CoSe2 /C nanospheres have great potential to serve as an electrode material for sodium-ion batteries.