Applications Of Nitrogen Doped Ti₃C₂T_x MXene In Li-S Battery And Aqueous Zn-ion Battery

It is extremely serious that the problems of energy exhaustion and environmental pollution leads to the large-scale combustion of fossil energy.People have converted the focus of energy development to clean energy such as solar energy,wind energy and nuclear energy.As an indispensable energy storage device,secondary battery can efficiently use clean energy.However,the current energy density of lithium-ion batteries can not meet people’s needs,various other systems of batteries,such as lithium-sulfur batteries,lithium-air batteries and zinc-ion batteries,have been gradually developed and utilized.In order to make various structures of batteries,many inorganic and organic materials have been applied in this field to realize the high energy density.The MXene materials have been widely applied in various fields because of their excellent two-dimensional surface,conductivity and adjustable functional group structure.These advantages also provide the possibility for its application in ion batteries.In order to solve the problems of poor cycle performance and slow redox kinetics in secondary batteries,this paper designed and prepared nitrogen doped MXenes materials and applied them to lithium sulfur batteries and aqueous zinc ion batteries.First,in order to solve the problems of shuttle effect and low electronic conductivity in lithium-sulfur batteries,the highly conductive nitrogen doped MXene material was introduced as the separator coating by means of blade coating.Through systematic research,its ability to adsorb and catalyze polysulfides was clarified,and the relationship between its microstructure and electrochemical performance was revealed.The assembled battery with nitrogen doped MXene coating separator showed a specific discharge capacity of 1336.8 mAh g^-1and a lower voltage hysteresis at a magnification of 0.1 C.The sulfur positive electrode can reach the initial specific capacity of 1012mAh g^-1at a high rate of 1 C and can cycle stably for 500 cycles.Under the condition of using high sulfur load 7.06 mg cm^-2,the assembled battery can still obtain 579.8 mAh g^-1specific discharge capacity,and 70.06%capacity retention rate within 150 cycles.In order to solve the problems of serious dendrite,side reaction and slow kinetics in zinc ion batteries,a nitrogen doped MXene（NMX）artificial interface layer was used to spin on the surface of zinc anode to protect zinc anode.The high conductivity of NMX can even the charge in the electric field on the surface of zinc anode.And through theoretical calculation,it was found that the adsorption of between nitrogen doped MXene and zinc was stronger than that of undoped MXene.At the same time,the desolvation ability of zinc ions on the negative electrode surface was also enhanced.Therefore,the artificial layer can induce the uniform deposition of zinc,inhibit the side reaction and accelerate the migration of zinc ions.The assembled symmetrical battery with NMX@Zn anode had a long cycle performance of 1900 hours and a low voltage hysteresis at a deposition capacity of 1 mAh cm^-2and a current density of 1 mA cm^-2.Assembled asymmetric cell NMX@Ti||Zn cycled steadily for 4800 cycles at a current density of 5 mA cm^-2and reached an average coulomb efficiency of 99.79%.The full cell which matched with Mn O₂anode can run 1000 cycles at a current density of 1 A g^-1and achieve a capacity retention rate of 80.1%.In conclusion,based on the excellent physical and chemical properties of nitrogen-doped MXene material,this paper designed a separator coating and an anode protection layer for lithium-sulfur battery and zinc-ion battery respectively,which improved the electrochemical performance of the two batteries.The role of NMX in the two kinds of batteries and its mechanism were summarized through a variety of experimental and theoretical calculation methods,which opened a new idea and way for the application of MXene based materials.