Design And Theoretical Investigation Of High-Performance Electrode Materials Based On Sulfur-Functionalized Mo₂NS₂

Efficient energy storage technology has always been a key factor limiting the development of new energy vehicles.Lithium-sulfur batteries,with their ultra-high theoretical energy density of2500 Wh/kg,are considered the most promising next-generation rechargeable batteries.However,the practical application of lithium-sulfur batteries is hindered by issues such as poor sulfur conductivity and the shuttle effect of lithium polysulfides.In comparison to lithium-ion batteries,other alkali metal ion batteries,such as sodium-ion and potassium-ion batteries,offer lower costs and more abundant resource reserves.Finding suitable negative electrode materials is a key aspect of achieving high-performance batteries in alkali metal ion batteries.To address these challenges,this study proposes the use of sulfur-functionalized transition metal nitride material（Mo₂NS₂）as the electrode material for batteries to enhance their electrochemical performance.The following research has been conducted:（1）Molecular dynamics simulations were performed on the Mo₂NS₂carrier and lithium polysulfide adsorbate.The carrier’s density of states was calculated using density functional theory,and system total energy calculations were conducted to determine the optimal adsorption configuration.The charge density difference and state density of the composite material after lithium polysulfide adsorption were also investigated.These calculations provided insights into the electronic and energy structures of the composite material after lithium polysulfide adsorption,enabling the exploration of its electrochemical and energy storage performance.The research results indicate that Mo₂NS₂,as a positive electrode material for lithium-sulfur batteries,exhibits excellent catalytic activity and adsorption performance,effectively adsorbing polysulfides,suppressing the occurrence of the shuttle effect,and improving the capacity retention and cycle life of lithium-sulfur batteries.This has significant implications for the practical application of lithium-sulfur batteries.（2）To gain a deeper understanding of the reaction kinetics of polysulfides on the carrier during the discharge process,the Gibbs free energy of all steps in the overall reversible reaction between elemental sulfur（S₈）and lithium metal to form Li₂S was calculated.By comparing the changes in Gibbs free energy,it is observed that the reduction steps from S₈to Li₂S₈,Li₂S₆to Li₂S₄,and Li₂S₄to Li₂S₂are exothermic reactions,with Gibbs free energy changes of-3.36 e V,-0.27 e V,and-0.6 e V,respectively.The other two reduction steps,from Li₂S₈to Li₂S₆and Li₂S₂to Li₂S,are endothermic reactions,with the step from Li₂S₂to Li₂S corresponding to the highest Gibbs free energy barrier（0.86 e V）,which limits the overall reaction rate.（3）The performance of Mo₂NS₂as a negative electrode material for metal-ion batteries(Li⁺,Na⁺,K⁺,Mg²⁺,and Ca²⁺)was investigated.The adsorption energies of metal ions on the Mo₂NS₂surface were calculated,and the optimal adsorption sites were determined.Additionally,the migration barriers of metal ions to neighboring sites were calculated.The computational results demonstrate that Mo₂NS₂exhibits favorable adsorption properties for different metal ions,with the highest adsorption strength observed for potassium ions,indicating a higher storage capacity on the Mo₂NS₂surface（adsorption energy of 2.34 e V）.Furthermore,different metal ions exhibit low migration barriers on the Mo₂NS₂surface,indicating that Mo₂NS₂is advantageous as a negative electrode material for metal-ion batteries to achieve high-performance battery performance.