Theoretical Study On The Effect Of?110?crystal Planes And Se Defects Of MoSe₂ On Its Performance As Anode Materials For Metal Ion Batteries

Rechargeable metal ion batteries play a vital role in modern transportation,communications and electronics industries.Their excellent energy density,service life and capacity make them the main power source for various portable electronic devices.Due to the advantages of two-dimensional materials such as good stability,high adsorption energy,rapid ion diffusion,and high storage capacity,they have gradually attracted researchers'attention as electrodes in high-performance rechargeable batteries.At present,the common commercial anode electrode material is graphite.Although its structure is very stable,its charging capacity is only 372 mAh/g,and the diffusion of ions on the graphite surface is not fast enough.In order to meet the rapidly growing market demand,people have begun to research and find anode materials that can replace graphite.As a new class of 2D materials,the excellent physical and chemical properties of transition metal di-chalcogenides?TMDs?have aroused great interest.As a representative material of TMDs,MoSe₂ has excellent electrochemical performance.The modification of its surface,including doping,creation of metastable crystal planes,vacancies,etc.,which can further improve the capacity and conductivity of materials,has also been widely concerned by experimental workers.Although the specific influence mechanism of the surface modification of related materials is crucial to the design of new materials,the corresponding theoretical research is incomplete.Therefore,in this paper,we discussed the effects of metastable crystal plane?110?and Se defects on the electrochemical performance of MoSe₂ for Li,Na,K,Mg and Al ions anode through first-principles calculations:?1?In order to explore the applicability of different crystal faces of MoSe₂ in rechargeable batteries,we calculated the material's open circuit voltage?OCV?curve,energy band structure,metal atom adsorption energy and diffusion energy barrier,etc.First-principles analysis shows that ionic bonds are formed between metal atoms and the base material,electrons are transferred from the metal atoms to the surface of the base material,and all systems become metallic after adsorbing metal atoms.The?001?crystal plane of MoSe₂ as anode materials for metal ion batteries shows very promising performance.Not only is the stability of the system not affected after the adsorption of metal atoms,but also the migration energy of atoms on the?001?crystal plane of MoSe₂ The barrier is also smaller than most 2D materials,and the corresponding OCV value is also in the low voltage platform range,which is very beneficial for the application of metal ion batteries.Compared with the?001?crystal plane,although the presence of the metastable crystal plane?110?will reduce the band gap and facilitate the adsorption of metal atoms,the diffusion of metal atoms becomes difficult,and the OCV value is also much higher,so it is not It is suitable for the negative electrode of most metal batteries.MoSe₂?110?is more suitable as the negative electrode material for Mg ion batteries because of its high adsorption energy and the ion migration energy barrier close to the?001?crystal plane.?2?Defect engineering has always been considered as an effective way to improve the electrochemical performance of materials.The MoSe₂ structure with Se defects has been successfully synthesized experimentally,but its application as an electrode material has not been reported.We mainly discuss the situation of single Se defect and double Se defect.Firstly,by calculating the adsorption energy to find the best site for metal atom adsorption,and then analyzing the electron transfer and migration efficiency,and finally by increasing the number of metal atoms adsorbed to calculate OCV.We found that the presence of Se defects can reduce the band gap of MoSe₂?001?,and the band gap value of the material decreases with the increase of the number of Se defects.The atoms interact strongly and accept electrons from these atoms efficiently.Due to the high OCV platform,Se-deficient MoSe₂ is not suitable as a negative electrode material for Li,Na,K,and Al ion batteries.But our results show that the Se defect MoSe₂?001?is very suitable for storing Mg atoms.Compared with the adsorption on perfect MoSe₂,the adsorption energy of Mg increases but the energy barrier changes little.This has positive significance for the design of new metal battery anode materials.