Design And Theoretical Study Of MXene-based Electrode Materials For Lithium-sulfur Batteries And Metal-ion Batteries

For sustainable development,developing clean energy is an inevitable choice.Energy storage technology plays a key role in the storage and utilization of clean energy.However,the capacity of commercial lithium-ion batteries is low.In response to this problem,researchers design lithium-sulfur batteries.Although lithium-sulfur batteries have advantages in energy density and theoretical capacity,problems such as poor sulfur conductivity,"shuttle effect"and volume expansion hinder their development.One of effective methods to solve these problems is to introduce host materials with high conductivity and suitable affinity to adsorb lithium polysulfides in the cathode.Considering the problems of low Li reserves and high cost,researchers turned their attention to other abundant elements,such as Na、K and Mg.They try to build new metal-ion battery systems with these elements.At present,finding suitable anode materials is one of the important tasks to develop new metal-ion batteries.In this paper,first-principles calculations are used to investigate the performance of Ti₂NS₂ as cathode materials for lithium-sulfur batteries and V₂CS₂ as anode materials for metal-ion batteries(Na⁺,K⁺,and Mg²⁺).The main research contents and conclusions of this paper are as follows:（1）Models of Ti₂N and V₂C are established.The structures of them are analyzed.Ti₂N and V₂C are hexagonal structures.Models of Ti₂NS₂ and V₂CS₂ are established based on Ti₂N and V₂C.The structural and electronic properties of Ti₂NS₂ and V₂CS₂ are studied.Ti₂NS₂ and V₂CS₂ are also hexagonal structures.The calculated results of density of states show that both Ti₂NS₂ and V₂CS₂are metallic.They are able to conduct electricity,which is a prerequisite for being electrode materials.（2）The performance of Ti₂NS₂ as cathode materials for lithium-sulfur batteries is studied.The adsorption properties,electronic properties,catalytic properties and Li migration properties of Ti₂NS₂ are analyzed.The adsorption results show that the adsorption energy of Ti₂NS₂ to lithium sulfur molecules is moderate,which is more stable than Ti₂NO₂.It can effectively suppress the"shuttle effect".The calculated results of density of states show that systems have electrical conductivity after the adsorption of lithium-sulfur molecules by Ti₂NS₂.The catalytic calculation results show that the Ti₂NS₂ surface can promote the progress of cathode reaction.The transition state calculation results show that the migration barrier of Li on the surface of Ti₂NS₂ is lower than that of Ti₂NO₂.Migration is fast.（3）The performance of V₂CS₂ as anode materials for metal-ion batteries(Na⁺,K⁺and Mg²⁺)is studied.The adsorption properties of V₂CS₂,the migration properties of metal ions and the theoretical capacity of V₂CS₂ are analyzed.The adsorption results showed that V₂CS₂ can stably adsorb Na⁺,K⁺and Mg²⁺.The systems still have electrical conductivity after the adsorption is completed.Transition state calculation results show that the migration barriers of Na⁺,K⁺and Mg²⁺on the surface of V₂CS₂ are low,especially Na⁺and K⁺.The theoretical capacity calculation results show that Na⁺and Mg²⁺have high storage capacity on the surface of V₂CS₂,while the theoretical capacity of K⁺ is relatively low.