First Principles Studies Of Two Dimensional V₂n Mxene Material For Secondary Battery Systems

The problem of environmental pollution and energy resource crisis have become increasingly serious in recent years.With the booming of new energy vehicles,smart grids and other large equipment,and the popularity of smart electronic products,the application of lithium ion battery has reached an unprecedented level under the situation of promoting "green and low carbon development".However,some typical problems,such as the potential safety problems of lithium ion batteries and the scarcity of lithium resources have not been solved,which urges people to explore and find new battery system with low price and excellent performance.Based on density functional theory,we used first-principles calculations to predict the performance indexes of electrode materials on the atomic scale,which provides a theoretical basis for us to explore new electrode materials and energy storage mechanism of secondary batteries.Synthesis technology is constantly updating.Two-dimensional materials have been extensively studied in the application of electrode materials for secondary batteries because of their unique layered structure,high specific surface area,rich reactive sites and good mechanical properties.MXenes are a class of two-dimensional layered transition metal carbon/nitrogen compounds with a wide varieties and excellent properties,which has attracted the attention of researchers.Vanadium-based materials have high charge/discharge capacity arising from the multi-electron redox chemistry of vanadium,and transition-metal nitrides provide higher conductivity than the corresponding carbides,which is desired in the battery applications.Therefore,in this paper,we calculated the structures and electrochemical properties of V2N,by first-principles calculations,predicting the two-dimensional V2N MXene to be a promising anode material for lithium ion batteries and beyond.We found that V2N monolayer is a metallic compound by first-principles calculations.The ions diffusion barriers on V2N monolayer are predicted to be 0.025 eV for Li ions,0.014 eV for Na ions,0.004 eV for K ions and 0.058 eV for Mg ions,which are very low for the most advanced two-dimensional energy storage materials.In addition,the calculated theoretical capacities are 925 mAh/g,463 mAh/g and 1850 mAh/g for Li,Na and Mg ions,respectively.The capacity of Li ions on V2N monolayer is much higher than that of Li ions on the conventional anode graphite,and the extra-large capacity for Mg ions on V2N monolayer is ascribed to the two-electron reaction and multilayer adsorption of Mg ions.Last,the average open circuit voltages are also calculated to be 0.32 V for Li ions,0.24 V for Na ions and 0.34 V for Mg ions.All these results indicating that two-dimensional V2N MXene monolayer is a promising candidate anode material for rechargeable lithium,sodium and magnesium ion batteries.