Experimental Investigation and First-Principles Calculations of a Ni₃Se₄ 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 Mg²⁺ 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, Ni₃Se₄ was first proposed as a new cathode material for MIBs. First-principles calculations showed that Ni₃Se₄ could accommodate up to 1 mol of Mg²⁺, but the migration energy barrier was as high as 1.35 eV. Accordingly, nanosized Ni₃Se₄ was prepared by a hydrothermal method to achieve satisfying electrochemical performance. The prepared Ni₃Se₄ material showed a discharge capacity of 99.8 mA·h·g^-1 at 50 mA·g^-1 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 Mg²⁺ insertion, with all charge transfer taking place on the Ni cations.