First-Principles Studies on High-Entropy Ti0.75V0.75Cr0.75Mo0.75C2 MXene Nanosheets as Anode Materials in Zinc-Ion Batteries

High-entropy MXenes as an emerging subfamily of MXenes have attracted great interest recently in the energy storage field, but the species are modest and related reports are scarce. Herein, the structural, electronic, and adsorption properties of a Ti0.75V0.75Cr0.75Mo0.75C2 high-entropy MXene nanosheet are investigated by density functional theory. The predicted dynamic and thermal stabilities indicate experimental feasibility. The Ti0.75V0.75Cr0.75Mo0.75C2 nanosheet exhibits strong conductivity before and after zinc-ion adsorption. Bilayer Ti0.75V0.75Cr0.75Mo0.75C2 possesses a large interlayer spacing so that it can accommodate a larger amount of zinc ions than bilayer Ti3C2. The effective interactions between zinc ions and bilayer Ti0.75V0.75Cr0.75Mo0.75C2 lead to high adsorption energies and realize the largest and average open circuit voltages (OCVs) of 1.18 and 0.63 V, respectively. With saturated zinc ions, the specific storage capacity of bilayer Ti0.75V0.75Cr0.75Mo0.75C2 reached 769.2 mAh/g. The calculated OCV and storage capacity are superior to those of Ti3C2. The calculated diffusion barriers between 0.18 and 0.29 eV besides the low mean square displacements and small diffusion coefficients indicate the fast kinetics processes of zinc-ion adsorption/desorption. The expansion ratio is merely 5.8%, suggesting a potential long lifetime, and it may realize large numbers of charge/discharge cycles without structural collapse. This work sheds light on the excellent electrochemical properties of the Ti0.75V0.75Cr0.75Mo0.75C2 nanosheet, which are universal for 2D high-entropy MXene family. These results will stimulate further theoretical and experimental studies on the electrochemical performance of 2D high-entropy MXenes.