Study On Modification Of Cathode Materials For Lithium Sulfur Battery By TiO₂

As a new type of lithium battery,lithium-sulfur battery has properties of high theoretical specific capacity and energy density,low price and environmental friendliness,and promising application.However,the battery has the problems during charging and discharging as follows:(I)the elemental sulfur and the discharged product of polysulfide are not electrically conductive,which results in an increase in the internal impedance of the battery,thereby it reduces the energy efficiency of the battery;(2)polysulfide dissolved in the electrolyte that produces the shuttle effect,which results in a great loss of battery capacity;(3)the volume of sulfur positive electrode changes greatly,which causes the structure of the positive electrode material to collapse and serious safety problems;(4)lithium negative electrode produces dendritic reaction,which make electrochemical performance dropped rapidly.Porous TiO2 material has high specific surface area and strong chemisorption property,the polysulfides may adsorbed physically and chemically on the surface of it,it inhibits the dissolution in the electrolyte.Therefore,the sulfur coating treatment by TiO2 is one of the effective ways to modify the cathode material of lithium-sulfur battery.To this end,porous TiO2 was prepared by anodic oxidation method followed by a freeze-drying process.In the porous structure,S was doped and the composite cathode material of TiO2/S was prepared.The microstructure and phase composition of the samples were characterized by XRD,SEM,XPS,EDS,etc.The samples were assembled into a button cell to test their electrochemical properties.The results of this paper are following:(1)Preparation and characterization of the electrochemical properties of the composite of TiO2 nanotube and S.In this paper,TiO2 nanotubes with both ends were prepared by anodization and heated under different atmospheres,then TiO2 and S were combined and which assembles battery as a positive electrode material,and its electrochemical performance was determined.The results show that TiO2 and S cathode materials treated at vacuum atmosphere are performed at a current density of 200 mA/g,the composite discharge capacity of TiO2 and S composite cathode has a first specific discharge capacity of 648 mAh/g,the capacity is 491 mAh/g after 50 cycles,and a capacity retention rate is 75.8%.The composite electrode of TiO2 and S treated at vacuum atmosphere has the best electrochemical performance.(2)Preparation and electrochemical performance of composite porous TiO2 and S composite cathode materials.The TiO2 porous ceramics were prepared by freeze-drying method,and which combined with sulfur to obtain TiO2/S composite cathode materials.The results show that When the mass ratio of small particle size(23 nm)to large particle size(300 nm)is 6:4,the composite primary cathode has a first discharge specific capacity of 964 mAh/g at 0.1 C rate,and the capacity is 628 mAh/g after 50 cycles,its capacity retention rate is 65.2%,and which has best cycle performance.