Preparation And Properties Of Cathode Materials For Ti₃C₂-based Lithium-sulfur Batteries By Molten Salt Method

Lithium-sulfur battery has been considered as an important secondary battery system with great development potential due to its high energy denstiy.However,some problems such as low electrical conductivity,serious volume expansion and the polysulfide shuttle effect charge and discharge restrict their application.Two-dimensional transition metal carbide-Ti₃C₂T_x,is a class of 2D materials with high electrical conductivity and good chemical stability,which show good capability to improve the electrochemical performances of lithium-sulfur battery.However,their traditional methods to prepare Ti₃C₂T_xare dangerous and environmentally unfriendly.Recently,molten salt etching method has attracted wide attention due to its green safety,high efficiency and universality.However,the preparation process of molten salt etching method is not mature enough.Moreover,there are few reports on the application of Ti₃C₂T_xprepared by this method in lithium sulfur batteries.In this paper,the Ti₃C₂T_xmaterials were prepared by the molten salt method,and the process parameters were optimized.Meanwhile,eutectic molten salt method by introducing NaCl into the molten salt system and high-temperature alkali treatment were further use to modify Ti₃C₂T_xmaterials.The main results are as follows:（1）The effects of reactant ratio,reaction temperature and reaction time on the structure of Ti₃C₂T_xmaterials prepared by molten salt method were investigated.When the reactant molar ratio is 1:6,reaction temperature is 600℃,and reaction time is 8 h,the prepared Ti₃C₂T_xmaterials show obvious overall layering,uniform layer thickness with interlayer spacing of 11.085（?）,and contain-Cl and-O termination groups.The Ti₃C₂T_x/S composite cathode prepared by the melt impregnation method exhibits a discharge specific capacity of 980 mAh·g^-1at 0.05 C;the capacity retention rates at 0.05 C and 0.1 C are 89.89%and 82.57%after 100cycles,showing better cycle performance than pure S cathode.（2）The p-Ti₃C₂T_xmaterials with the larger specific surface area were synthesized by using eutectic mixed molten salt NaCl/ZnCl₂as the etchant.Compared with the Ti₃C₂T_xmaterials prepared with single molten salt,the obtained p-Ti₃C₂T_xmaterials show larger specific surface area with more uniform and thinner layer.The p-Ti₃C₂T_x/S composite cathode exhibit a specific discharge capacity of 1077.4mAh·g^-1at 0.05 C and a capacity retention of 92.52%after 100 cycles,indicating better electrochemical performances than that of Ti₃C₂T_x/S cathode.Meanwhile,the p-Ti₃C₂T_x/S cathode also exhibits better rate capability.（3）The Ti₃C₂-C materials were prepared by heat-treated Ti₃C₂T_xwith molten KOH.The Ti₃C₂layer is further exfoliated due to the intercalation of K⁺,and the interlayer spacing increases to 12.309（?）.The Ti₃C₂-C/S composite cathode exhibits a high discharge specific capacity of 1202.9 mAh·g^-1at 0.05 C and a high capacity retention of 96.01%under 100 cycles.Moreover,it also displayed supiror rate performance compared with that of Ti₃C₂T_x/S cathode.