Theoretical Study Of Two-dimensional Metal Compound Electronic Devices

The rechargeable battery is an important energy storage device of our daily lives.As a rechargeable battery,lithium-ion batteries are widely used in mobile phones,laptop computers,electric vehicles,solar power stations and other energy storage power system due to their advantages of high energy density,large output power,many cycles,no memory effect,green and environmental protection.However,electrode materials have a great influence on the performance of lithium-ion batteries.The disadvantages of low safety,low charging rate,and relatively high cost limit the development of lithium-ion batteries.Therefore,research on electrode materials with new structure and performance is of great significance to improve the performance of lithium ion batteries.Since the discovery of graphene,two-dimensional materials have achieved rapid development,providing almost all the electronic characteristics required by nano-electronic devices.Two-dimensional materials have excellent physical and chemical properties such as small size,high specific surface area,large mechanical strength,and easy adjustment.They are ideal materials for many fields such as ion batteries,optoelectronic devices,sensors,and spintronics.Theoretical calculations can predict and verify the properties of two-dimensional materials,and theoretical research as a guide can greatly improve experimental efficiency.Guided by density functional theory,this paper theoretically predicts the feasibility of the application of new two-dimensional metal compound materials in electronic devices through first-principles calculation methods.The main contents are as follows:?1?The feasibility of new two-dimensional transition metal borides?TMBs?as anode materials for LIBs/NIBs was explored.It mainly calculates the electronic structure,adsorption energy,diffusion energy barrier,open circuit voltage and storage capacity.The transition metal boride has an orthogonal structure and exhibits excellent electrical conductivity characteristics.Li/Na atom forms stable adsorption on the transition metal boride surface,and the diffusion energy barrier is much lower than commercially available electrode materials.More importantly,the high stoichiometric ratio?TMBLi₂/TMBNa₂?results in high storage capacity.Therefore,two-dimensional single-layer transition metal borides,especially 3d orbital transition metals,should be ideal for large-capacity LIBs/NIBs.?2?It is proposed that the multi-active center of the two-dimensional lithium ion battery anode material can greatly improve the storage capacity.Two-dimensional transition metal nitrides and their surface functional groups possess unique electrochemical properties that affect ion adsorption,diffusion,and electronic properties.Studies have found that Cr₂NH₂ shows structural stability and metallicity before and after the adsorption of lithium atoms.Both Cr and N atoms can form strong adsorption behavior with lithium atoms.This unique multi-active center and multilayer adsorption behavior greatly improves lithium storage.The capacity(822 m Ah g^-1)is almost the highest among two-dimensional transition metal compounds.Simultaneous calculation results show that lithium has a low diffusion energy barrier?0.085 eV?and an open circuit voltage?0.53 eV?on the Cr₂NH₂monolayer.Therefore,the synthesis of two-dimensional transition metal compounds with higher covalent properties will have broad prospects for the development of high-performance lithium-ion battery anode materials.?3?It was found that the external electric field produced a huge band gap modulation of the indium halide InX?X=Cl,Br,I?single layer,realizing the insulator-metal transition,which can be used to design new field effect transistors.The theoretical calculation results show that due to the relatively low peel energy,the single layer of indium halide can be easily peeled from its three-dimensional bulk structure.At the same time,due to the ionic characteristics of the In-X bond and weak electrostatic shielding effect when an electric field is applied,a huge band gap modulation is achieved,and the effective factors??E_g/U?of the single-layer InCl,InBr and InI are 0.90,0.88 and0.78,which is much higher than any previous reports.In addition,for the InI bilayer and four layers,the energy gap can be easily closed by the actual electric field,and the critical electric fields of the closed band gap are only 0.3 V/?and 0.1 V/?,respectively.Therefore,ionic semiconductors with large effective factors are expected to play their potential in the future development of high-performance devices.