Investigation On Preparetion And Electrochemical Performance Of Cathode Based On MWCNTs And PANI In Li-S Battery

Lithium-sulfur（Li-S） battery has attracted much attention in recent years for the low cost, abundance of sulfur, environment friendliness, high theoretical specific capacity（1675 mAh/g） and energy density（2600 Wh/kg） of sulfur cathode. However, the practical application of Li-S battery is inhibited by several problems, including the low conductivity of sulfur and Li2 S, the shuttle effect and the large volume expansion rate of sulfur during the charge-discharge process. To solve these problems, we investigate the preparation and electrochemical performance of cathode based on MWCNTs and PANI in Li-S battery.A core-shell S/MWCNTs cathode material is prepared through ball milling and thermal treatment. Then the in situ chemical oxidation polymerization of lolyaniline was carried out to obtain the dual core-shell PANI/S/MWCNTs. Thermogravimetric（TG） analysis shows the content of sulfur in PANI/S/MWCNTs which is 68%. The initial discharge capacities of the PANI/S/MWCNTs composite is 1151 mAh/g at 0.2 C. After 80 cycles, a high reversible capacity of 835 mAh/g is obtained, corresponding to capacity retention of 72.2%. Characterized by Scanning Electron Microscope（SEM）, Transmission Electron Microscopy（TEM）, Fourier Transform Infrared Spectroscopy（FTIR） and Electrochemical Impedance Spectra（EIS） analysis, the PANI coating layer proves to be uniform, which can not only improve the conductivity, but also localize and retain dissolved intermediate polysulfides during cycling.The PANI nanofibers are synthesized by a severe chemical oxidation of aniline and ammonium peroxydisulfate. Then the PANI nanofibers are heated to obtain the carbonized PANI(C_PANI). The CNTs bristles grow on the surface of C_PANI through CCVD and obtain the C_PANI-CNTs. The initial discharge capacities of the C_PANI-CNTs-S composite is 1094 mAh/g at 0.5 C and 941 mAh/g at 1 C. After 150 cycles at 0.5 C, a high reversible capacity of 711 mAh/g is obtained, corresponding to capacity retention of 65%. After 300 cycles at 1 C, a high reversible capacity of 654 mAh/g is obtained, corresponding to capacity retention of 64%. The CNTs cannot only increase the electronic conductivity and the transmission of Li+ which will improve the utilization of sulfur and the high rate performance, but also localize and retain dissolved intermediate polysulfides during cycling which can suppress the shuttle effect.