Copper Doping of CoSe₂ Nanoparticles Encapsulated into Carbon Nanotubes with Enhanced Electron Conductance as Cathode for Rechargeable Magnesium Batteries

Abstract Rechargeable magnesium batteries (RMBs) have been considered a promising alternative to lithium‐ion batteries (LIBs) due to the high energy density and abundance of magnesium resources. However, the development of high‐performance cathode materials for magnesium batteries has been a significant challenge. Herein, through comprehensive and simple hydrothermal, selenization and impregnation methods, Cu‐doped CoSe₂ nanoparticles encapsulated into carbon nanotubes (Cu‐CoSe₂@NC) was fabricated. CoSe₂ nanoparticles confined in carbon nanotubes (CNTs) growing in three dimensions on the surface of nanofibers have abundant active sites and high doping degree. Cu doping further improves the electron conductance of the Cu‐CoSe₂@NC for RMBs. As cathode, Cu‐CoSe₂@NC delivers a reversible capacity of 294 mAh g⁻¹ at 20 mA g⁻¹ and 104 mAg g⁻¹ at 500 mA g⁻¹, which exhibits a reasonable specific capacity and rate capability. The characterization of the Cu‐CoSe₂@NC by ex‐situ transmission electron microscopy (TEM) after cycles shows that it can be well adapted to the (de)intercalation of magnesium ions. Density Functional Theory (DFT) calculation shows that CoSe₂ band gap decreases obviously after Cu doping, favoring the electron and ion transport. This work provides a reference for the design of cathode materials based on transition metal selenide for RMBs.