First-Principles Study Of Li-Ion Adsorption Behavior On Janus MoSSe

Lithium-ion batteries owing to the advantages of light weight,large capacity and no memory effect are widely used in portable electronics and electric vehicles.Anode materials are crucial to the electrochemical performance of lithium-ion batteries(LIBs).However,the low capacity and poor stability of anode electrode materials limits the use of LIBs.Therefore,it is the key to development high-performance anode materials.In recent years,transition metal dichalcogenides(TMDs)have attracted research interest in energy conversion and catalysis due to their unique physical properties and excellent performance.Such as,TMDs enable fast lithium ions transport due to their large layer spacing.Compared with the common H and T phases,the S phase is rarely studied.Furthermore,the effect of strain on the electrochemical properties is unclear.Here,we studied the adsorption properties of lithium ions on Janus MoSSe monolayers by the first-principles computational approach.The research work is divided into three parts:(1)We investigated the adsorption properties of monolayer H-phase MoSSe on lithium ions under zero-strain conditions.It was found that on the 1H-MoSSe surface,lithium ions have three stable adsorption sites on the Se side and S side,respectively,where the lithium ions are most stably adsorbed on top of the Mo on both sides,and the binding on the S side is stronger than on the Se side.We investigated the migration paths and migration energies of lithium-ion on the 1H-MoSSe surface using transition state calculations,and found that the lithium ions migrate from the TMo site to the adjacent TMo site via the H site in a V-shaped migration path with energy barriers of 0.24 eV and 0.29 eV on the Se and S sides,respectively.In addition,1H-MoSSe has a high capacity and a low opencircuit voltage.(2)We explored the adsorption properties of 1S-MoSSe on lithium ions under zero-strain conditions.On the 1 S-MoSSe surface,the calculated results show that the single Li atom is energetically more inclined to adsorb at the central position(O site)and the S layer side of the octagonal ring of 1 S-MoSSe.The predicted surface energy barriers for Li diffusion range from 0.33 to 0.51 eV,and the kinetics of Li migration on 1 S-MoSSe are accept.Further adsorption thermodynamic analysis showed that the lithification process before the Li concentration x=1.0 was stable,on top of which the lithification process became unstable and with a negative charge potential.Phonon calculations confirmed that Li adsorption(0.25≤x≤0.75)causes lattice distortion of 1 S-MoSSe,thereby inhibiting structural instability.Although the dipole moment of 1 S-MoSSe is higher,1 S-MoSSe will be unstable at lower lithium concentrations compared to 1S-MoS2 and 1H-MoSSe,which can be attributed to the asymmetric nature of 1 S-MoSSe.(3)We studied the mechanochemical coupling properties of Janus MoSSe,and we found that lithification deteriorated the mechanical properties of the structure to varying degrees,but proper strain can stabilize the lithified structure.Then we calculated the state density and d-band center of H-MoSSe,Li1H-MoSSe and Li6H-MoSSe under strain conditions,and found that the electronic band gap width decreased with the increase of strain when Li ion adsorbed,and the center of the d-band first decreased and then rose.In the adsorption structure,as the valence band of the stress increases significantly,the corresponding center of the d-band gradually rises.