Electronic structure engineering on NiSe micro-octahedra via nitrogen doping enabling long cycle life magnesium ion batteries.

Multivalent ion batteries have attracted great attention because of their abundant reserves, low cost and high safety. Among them, magnesium ion batteries (MIBs) have been regarded as a promising alternative for large-scale energy storage device owing to its high volumetric capacities and unfavorable dendrite formation. However, the strong interaction between Mg and electrolyte as well as cathode material results in very slow insertion and diffusion kinetics. Therefore, it is highly necessary to develop high-performance cathode materials compatible with electrolyte for MIBs. Herein, the electronic structure of NiSe micro-octahedra was modulated by nitrogen doping (N-NiSe) through hydrothermal method followed by a pyrolysis process and this N-NiSe micro-octahedra was used as cathode materials for MIBs. It is worth noting that N-NiSe micro-octahedra shows more redox active sites and faster Mg diffusion kinetics compared with NiSe micro-octahedra without nitrogen doping. Moreover, the density functional theory (DFT) calculations indicated that the doping of nitrogen could improve the conductivity of active materials on the one hand, facilitating Mg ion diffusion kinetics, and on the other hand, nitrogen dopant sites could provide more Mg adsorption sites. As a result, the N-NiSe micro-octahedra cathode exhibits a high reversible discharge capacity of 169 mAh g at the current density of 50 mA g, and a good cycling stability over 500 cycles with a maintained discharge capacity of 158.5 mAh g. This work provides a new idea to improve the electrochemical performance of cathode materials for MIBs by the introduction of heteroatom dopant.