Study Of Carbon Fiber As Conductive Agent Of Cathode Materials For Lithium-Sulfur Batteries

Because of the advantages of the high theoretical specific capacity, theoretical energy density and wide range of sources, lithium-sulfur batteries has become a large potential chemical power. But its wider application is limited by the poor electrical conductivity of sulfur and the fast fading capacity. First the micron high modulus carbon fiber(BHM3) was prepared by ductile, then sulfur cathode composites with polyethylene glycol (PEG) coating was prepared using the PEG-coated method. The materials was evaluated with XPS, EDS, SEM, XRD, contact angle, aspiration rate, rate capability, cycle performance, cyclic voltammetry and AC impedance and other aspects of the performance test. The test results are as follows:(1) When acetylene black (AB), BHM3 and their composite was used as the sulfur positive electrode conductive agent, SEM results showed micron BHM3 can be uniformly distributed in the sulfur cathode materials, and the aggregation problem of nanofibers does not appear. The capacity holding for electrolyte analysis shows that the composite of aspiration rate is higher than the single conductive agent. XPS results show that the higher oxygen content, the higher the aspiration rate. The electrochemical results show that:composite containing the conductive agent AB and BHM3 sulfur composite has a higher initial specific capacity 1010mAh g"1 and good cycle life. AC impedance test results capacity 1010mAh g-1 and good cycle life. AC impedance test results show that the impedance of sulfur cathode with AB and BHM3 conductive agent composite is minimized. Therefore, AB and BHM3 compound as the positive electrode conductive agent was the best selection.(2) The sulfur composite positive electrode with PEG coating was prepared. The results of different concentrations of PEG4000 showed that the content of PEG coating has also made 0.075% to 2.28%, with the PEG-coated concentration from 1% to 10%. Contact angle and aspiration rate tests show that with the increase in material surface coating of PEG coating material wettability changed for the better, aspiration rate increases. When the PEG coating content is 1.09%(6% concentration of PEG-coated), the rate performance and cycle performance of the material are all the best. The initial specific capacity was increased from 974.3mAh g-1 to 1312.5mAh g-1 and the capacity remained at 650mAh g-1 after 50 cycles. In addition, the resistance of the material is also the smallest. When the cathode was coated by PEG with different molecular weight, the sample with PEG2000 has the smallest contact angle and the biggest aspiration rate. The rate performance and cycle performance of the material are all the best, and the capacity maintained a high 700mAh g-1 after 50 cycles. The performance of the material was the best when the material was coated by the concentration of 6%(Wt) PEG2000. Finally, the effects of different electrical conductivity carbon fiber BHM3 and M55J conductive agent were studied. The results show that the performance of conductive agent M55J is better than that of conductive agent BHM3.