First-Principles Studies on High-Entropy Ti_0.75V_0.75Cr_0.75Mo_0.75C₂ MXene Nanosheets as Anode Materials in Zinc-Ion Batteries

Abstract

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.

High-Capacity V2N MXene for Multivalent Ion Batteries: An Ab Initio Study

“…The energy reaches a minimum when the Zn/Ca ion is positioned precisely at the final position, as depicted in Figure . For Zn and Ca ions, the observed diffusion barrier is low as compared to previously reported MXene-based studies. , A low migration energy barrier implies a simpler transfer process and fast charging and discharging electrochemical properties.…”

“…4−7 Among these alternatives, zinc-and calcium-ion batteries (CIBs) have taken the spotlight in research due to their cost-effective manufacturing, low redox potential, nontoxicity, high theoretical capacity over Li-ion, Na-ion, Mg-ion, and Al-ion batteries. 8,9 MXenes, a class of novel two-dimensional (2D) material consisting of transition-metal nitrides and carbides, due to their superior electrical conductivity, thermodynamic stability, tunable surface features, and layered structure, have been extensively researched and acknowledged for energy storage. Their hydrophilic nature and adjustable surface chemistry allow for diverse functionalities.…”

“…Several potential replacements for lithium-ion batteries such as sodium, potassium, magnesium, aluminum, calcium, and zinc-ion batteries (ZIBs) have attracted significant attention due to their cost-effectiveness, safety features, eco-friendliness, and abundant availability. , Moreover, multivalent ions (Zn 2+ , Ca 2+ , and Mg 2+ ) have the capability to furnish a larger quantity of electrons in a single redox process compared to monovalent ions like Li + , Na + , and K + . This property results in a superior volumetric energy density for multivalent ions when compared to Li + . − Among these alternatives, zinc- and calcium-ion batteries (CIBs) have taken the spotlight in research due to their cost-effective manufacturing, low redox potential, nontoxicity, high theoretical capacity over Li-ion, Na-ion, Mg-ion, and Al-ion batteries. , …”

Advanced Insights on MXenes: Categories, Properties, Synthesis, and Applications in Alkali Metal Ion Batteries

“…Mo 2 CT x as an anode of LIB possesses higher theoretical capacity (526 mAh g –1 ) and greater thermal stability than those of Ti 3 C 2 , which is beneficial to maintaining the structural stability in LIBs . Recently, high-entropy MXenes formed by multiple metal elements, such as TiVNbMoC 3 , Ti 0.75 V 0.75 Cr 0.75 Mo 0.75 C 2 , and Ti 1.1 V 1.2 Cr 0.8 Nb 1.0 Mo 0.9 C 4 T x , exhibited superior ion storage performance compared to that of single-metal MXene due to high electrical conductivity originating from the electron redistribution of multimetal quasi-atoms and rich active sites of multiple metal atoms. However, there are few reports about the utilization of high-entropy MXenes as electrodes in alkali ion batteries.…”