Synthesis And Electrochemical Lithium Storage Performance Of Magneli Phase Ti_nO_2n-1 Based Composite Cathodes

In recent years, lithium-sulfur (Li-S) batteries have attracted considerable interests as the secondary batteries. However, Li-S batteries suffer from two major issues. One is the insulating nature of S, the other is the "shuttle" effect happened during the electrochemical reaction. Which leading to a significant loss of S during cycling, and a low coulombic efficiency of the Li-S batteries. Many strategies have been used to address these problems, and remarkable improvement have been achieved. However, at present, researches on using Magneli phases Oxides composies as cathode material is still at a very early stage. Compared with normal oxides and porous carbon materials, Magneli phases TinO2n-1with nano-structure has unique advantages:①Higher electronic conductivity and electrochemically stablity;②With the great number of missing oxygen atoms, Li2Sn could be further absorbed or dissociated by Magneli phases Oxides, as well as the physical absorption. So the "shuttle" effect could be restrained. In this paper, Magneli phases TinO2n-1with different n have been synthesized and used as conductive matrix in Li-S and Li-Se batteries.(1) Magneli phases TinO2n-1were synthesized by multistep method. TiO2nanotubes coated by SiO2were heated at different temperatures in pure hydrogen for different times. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). Ti6O11nanorods were synthesized at950℃in pure hydrogen for4h, with a size of5～10nm in diameter and50～100nm at length; while Ti4O7nanoparticles were synthesized at1050℃in pure hydrogen for4h, with a uniform size of300nm.(2) Ti4O7@S、Ti6O11@S、TiO2NT@S were synthesized by heat treatment. The electrochemical tests indicated that Ti4O7@S delivers an initial discharge volumetric capacity density of2471.6mA/cm3at the first cycle, which was the highest capacity density in these composites; excellent cycling performance (a reversible capacity of1086.6mA/cm3is obtained after250cycles at0.5C. The capacity retention rate is97%). The characterization of XRD、TEM、 EDS、non-suit XPS、in-suit XRD、Raman、TGA indicated the absorption theory of Li2Sn(3) Ti4O7@Se and MWNT@Se were synthesized by heat treatment. The electrochemical tests indicated that Ti4O7@Se delivers an initial discharge capacity density of424.6mAh/g (at rate of50mA/g, composites) at the first cycle, which is higher than MWNT@Se, and maintains a reversible capacity of350mAh/g((at rate of100mA/g, composites) after50cycles.