Experimental Investigation and First-Principles Calculations of a NiSe Cathode Material for Mg-Ion Batteries.

Magnesium ion batteries (MIBs) have attracted increasing attention due to their advantages of abundant reserves, low price, and high volumetric capacity. However, the large Coulombic interactions of Mg with the cathode framework seriously hinder the rate capability and cycle stability of the battery cell. For this reason, finding a suitable cathode material has become a main task in MIB research. In this study, NiSe was first proposed as a new cathode material for MIBs. First-principles calculations showed that NiSe could accommodate up to 1 mol of Mg, but the migration energy barrier was as high as 1.35 eV. Accordingly, nanosized NiSe was prepared by a hydrothermal method to achieve satisfying electrochemical performance. The prepared NiSe material showed a discharge capacity of 99.8 mA·h·g at 50 mA·g current density with a capacity retention of 75% after 100 cycles. Combined with first-principles calculations and spectroscopic studies, it was demonstrated that the material underwent a solid-solution structural change during Mg insertion, with all charge transfer taking place on the Ni cations.