| Lithium-ion batteries are widely used in electronic devices,electric vehicles and smart grid systems because of their advantages such as no memory effect and good cycle stability.However,the development of lithium-ion batteries has been constrained by factors such as low capacity,slow charging and discharging rates,and low lithium reserves.Therefore,researchers have been searching for electrode materials with excellent performance on the one hand,and actively exploring other metals to replace lithium in ion batteries on the other.In particular,the abundant reserves and low cost of sodium and potassium ion batteries and multivalent ion batteries.Because the electrons of two-dimensional materials are bound in the plane,they have the advantages of large specific surface area,high mobility and easy regulation,and have broad application prospects in ion batteries,electronic devices and spintronics.In this paper,the performance of two-dimensional γ-XY(X=Si,Ge;Y=S,Se)and Cr3C2 monolayers and its derivatives as electrode materials for ion batteries is investigated in terms of structural stability,electromagnetic properties,adsorption and diffusion properties,and capacity through firstprinciples calculations,mainly as follows:(1)The intrinsic structure and electrical properties of two-dimensional γ-XY are investigated.Firstly,the thermodynamic and mechanical stability of the two-dimensional γ-XY structure is demonstrated in terms of binding energy,phonon spectrum and molecular dynamics as well as mechanical properties.Secondly,the electronic structure of the two-dimensional γ-XY and the modulation of the electric field and strain are analyzed.The intrinsic γ-XY monolayers are all of indirect bandgap semiconductor nature,while the bilayers γ-SiS and γ-SiSe are of metallic nature.Meanwhile,it is found that the electric field and strain can regulate the electrical properties of two-dimensional γ-XY.Finally,the carrier mobility of two-dimensional γ-XY is calculated.The results show that the electron mobilities of monolayer γ-SiSe and γ-GeSe in the x-direction are 1281.25 cm2V.ls’1 and 1553.88 cm2V-1s-1,respectively.The electron mobilities of bilayer γ-GeSe is as high as 3115.25 cm2V-1s-1 in the x-direction and γ-directional mobility of 1112.23 cm2V-1s-11,which is much higher than that of the common MoS2(200 cm2V-1s-1)and has great potential for high performance electronic devices.(2)The application prospects of two-dimensional γ-XY in ion battery electrodes are explored.The feasibility of γ-XY as an electrode material for ion batteries is discussed in terms of ion adsorption and diffusion,open-circuit voltage,and capacity.The calculated results show that γ-SiS has a capacity of 893.37 mA h g-1 and diffusion energy barriers of 0.13 eV and 0.12 eV as an electrode for Li and Ca ion batteries,while γ-SiSe has a capacity of up to 1503.42 mA h g1 as an electrode for Ca ion batteries.in addition,the open-circuit voltage of γ-XY ranges from 0.04 V～0.72 V.In conclusion,two-dimensional γ-XY is an ideal electrode material for Li and Ca ion batteries.(3)The feasibility of two-dimensional Cr3C2 and Cr3C2T2(T=F,Cl,O,OH)as electrode materials for ion batteries is predicted.First,the structural stability and electromagnetic properties of two-dimensional Cr3C2(T2)are analyzed.The kinetic and thermodynamic stability is demonstrated by calculating phonon spectra and molecular dynamics.Meanwhile,Cr3C2(T2)exhibits metallic or semi-metallic properties,indicating its good electrical conductivity.Secondly,the adsorption and diffusion properties of different metal atoms on the surface of Cr3C2 and its derivatives are investigated.Among them,the Cr3C2 has a low diffusion energy barrier on it,and the energy barriers of Li and Na are 0.02 eV and 0.01 eV.Finally,the open-circuit voltages and capacities of Cr3C2 and its derivatives are calculated.The results show that the ions other than K can achieve multilayer adsorption and provide open-circuit voltages of 0.07 V～1.01 V.Among them,Li can adsorb 2 layers on the Cr3C2 and Cr3C2O2 with capacities of 595.58 mA h g-1 and 505.68 mA h g-1,while multivalent Mg and Al ions can adsorb 2～3 layers on the monolayer of Cr3C2 and Cr3C2O2 with capacities up to 1786.73 mA h g-1.Therefore,Cr3C2 and its derivatives are potential electrodes for a new generation of ion batteries materials. |
