Design And Property Studies On Novel Twodimensional Transition Metal Compound For Anode Materials

Layered structure of two-dimensional(2D)transition metal compounds,because of its unique physical and chemical properties,electrochemical storage in photocatalytic thermoelectric biosensor etc.,showed great potential applications in a broad range of areas.Especially as the electrode material,the larger layer spacing and specific surface area,the higher conductivity coefficient of thermal conductivity and mechanical strength,make it become the research hot spot.In order to screen and develop more excellent transition metal compound anode materials,this paper firstly uses CALYPSO package which based on particle swarm optimization algorithm to search the2D structures of transition metal(TM=V,Zr,Nb)carbide and nitride with the ratio of the chemical formula TM:C/N=1:1,and obtains multiple possible 2D crystal structures(TMCs and TMNs are used to represent transition metal carbide and nitride,respectively).After further structural optimization,the crystal configuration with the lowest energy was obtained,and it was found that all the crystal configurations of TMCs and TMNs were tetragonal structures,P4/nmm space group(no.129).Based on all the predicted 2D structures,we selected vanadium carbide and vanadium nitride(tetr-V₂C₂ and tetr-V₂N₂)with the lowest adsorption energy for Li atoms,and studied their performance as anode materials for lithium ion batteries.Firstly,the structural stability of tetr-V₂C₂and tetr-V₂N₂ was verified to meet the practical application of electrode materials.By comprehensively considering the cohesive energy,phonon dispersion curve,mechanical properties,free energy and radial distribution function of the system under high temperature,it is found that tetr-V₂C₂ and tetr-V₂N₂ show good lattice stability and can be used as independent thin film materials.Secondly,by calculating the energy band and electron state density of tetr-V₂C₂ and tetr-V₂N₂,it can be found that they exhibit inherent metal properties and still maintain metal properties in the lithium process.Finally,the adsorption and diffusion behaviors of Li on 2D tetr-V₂C₂ and tetr-V₂N₂ surfaces show high Li capacity,low Li diffusion rate and open circuit voltage.All the results show that tetr-V₂C₂ and tetr-V₂N₂ are promising anode materials for Li-ion batteries.This is very important and shows that our predicted 2D TMCs and TMNs systems offer an unprecedented opportunity for the development of high-performance electrode materials.In addition,in order to know the suitable substrates for the synthesis of these new 2D materials by chemical vapor deposition(CVD),several kinds of common substrates were selected for research,and the optimal substrates were obtained,which provided theoretical guidance for experimental selection.Based on the predicted 2D systems,a new class of transition metal boron nitrogen compounds(TM₂BN,TM=Ti,V,Zr,Nb)was designed by"atomic substitution"strategy.Further DFT calculations revealed that Ti₂BN exhibited better performance than tetr-V₂C₂ and tetr-V₂N₂ in the application of anode materials.Its Li capacity,Li diffusion rate and open circuit voltage are obviously better than tetr-V₂C₂ and tetr-V₂N₂.In addition,the structural stability of Ti₂BN are the same as that of tetr-V₂C₂ and tetr-V₂N₂,with sufficient plane stiffness.Similarly,through theoretical test,it is concluded that Ag(100),Au(100)and Sn(100)can be used as growth matrix for experimental synthesis.Furthermore,based on the application prospect of 2D transition metal disulfide compounds(TMDs)in electrochemical energy storage,another ordered metallic dual transition metal sulfide(TiNbS4)was designed.It has a sandwich crystal structure similar to 2D transition metal disulphoride(TMDs),but unlike most TMDs show semiconductor properties,it exhibits good metallic properties.This makes it possible for it to become a cathode material.Therefore,in order to verify the potential of TiNbS₄ as a negative electrode material,the DFT calculation was carried out.The results show that its low Li diffusion barrier,high Li diffusion coefficient and theoretical capacity,as well as low mean open circuit voltage make it have real potential in the application of negative electrode materials.In conclusion,three kinds of 2D transition metal compounds(TMCs and TMNs,TM₂BN;TiNbS₄)were designed theoretically and verify their application value in Li-ion anode materials.This provides guidance for the search and screening of new advanced anode materials and provides an unprecedented opportunity for the development of the next generation of anode materials.