Study On Ti₃C₂T_x Mxene Its Derivatives In Suppressing Shuttle Effect Of Lithium-sulfur Batteries

Facing the depletion of fossil fuels and the environmental pollution caused by their use,the development of renewable clean energy has attracted more and more attention.An important link to promote the development of clean energy is to develop an energy storage system that is economical,environmentally friendly,high energy density,and long service life.Lithium-sulfur batteries have the characteristics of high theoretical energy density(2500Whkg^-1),low cost,and environmental friendliness,so they are very promising energy storage devices.However,due to the effects of the insulation of sulfur,electrode volume expansion during discharge,and the shuttle effect of polysulfides(Li PSs),the rate performance and cycling performance of lithium-sulfur batteries are not satisfactory.In order to improve the electrochemical performance of lithiumsulfur batteries,this paper separately studied Ti₃C₂T_x(T stands for-F,-O and-OH groups)on the cathode and TiN@C on the separator coating of the batteries.The main contents are as follows:(1)Ti₃C₂T_x-CB/S cathode material was prepared by mixing 2D Ti₃C₂ Tx nanosheets and carbon black/sulfur(CB/S)composite,and then coated on a commercial separator(PP)to produce Ti₃C₂T_x-CB/S-PP electrode with the integration of cathode and separator.By introducing the Ti₃C₂ Tx nanosheets into the CB/S particles,multiple Li PSs blocking and adsorption regions are constructed,so that Ti₃C₂T_x can not only spatially inhibit the diffusion of Li PSs dissolved in the electrolyte,but also can anchor Li PSs through chemical interactions.In addition,the excellent electron transport ability of Ti₃C₂T_x is beneficial to accelerate the reaction kinetics of the cathode and the design of the integrated electrode increases the energy density of the battery.Lithium-sulfur batteries based on Ti₃C₂T_x-CB/S-PP have an initial discharge capacity of 1028.8mAhg^-1 at 0.1C,and can maintain a discharge capacity of 465.1mAhg^-1 after400 cycles at 0.5C with a capacity decay rate of 0.072% per cycle.(2)2D TiN@C was obtained by sintering Ti₃C₂ Tx in ammonia gas,and then it was mixed with graphene.Finally,TiN@C/G coated separator was prepared by vacuum filtration.TiN@C can produce strong chemical adsorption for soluble Li PSs and catalyze their conversion into insoluble Li₂S₂/Li₂S solids.Besides,the flaky structure of TiN@C allows the rapid transfer of Li+.In addition,the graphene in the coating can physically intercept the shuttled Li PSs and its high conductivity facilitates the activation of Li₂S during charging.Therefore,the TiN@C/G separator coating not only inhibits the shuttle effect,but also acts as an additional current collector to improve the utilization of active material.Lithiumsulfur batteries based on TiN@C/G-coated separator and CB/S cathode exhibite excellent electrochemical performance.The initial discharge capacity at 0.1C is as high as 1490.2mAhg^-1.A discharge capacity of 882.9mAhg^-1 is obtained at 1C and 635.8mAhg^-1 remains after 600 cycles with a capacity decay rate of 0.047% per cycle.