Improvement of Rate and Cycle Performence by Rapid Polyaniline Coating of a MWCNT/Sulfur Cathode

Rapid in situ chemical oxidation polymerization of polyaniline was carried out to coat MWCNT-core/sulfur-shell structures. The S-coated-MWCNTs were obtained by ball-milling and thermal treatment. The polymerization was carried out by adding 2.6 g of dispersed S/MWCNT and 0.65 g of aniline hydrochloride to ethanol, and then mixing in a certain amount of ammonium peroxydisulfate dissolved in 0.2 M HCl. The addition of S/MWCNT reduced the polymerization time from 60 to 21 min. The composites were characterized by elemental analysis, FTIR, XRD, SEM, TEM, and electrochemical methods. A 70.0% sulfur, 20.2% emeraldine PANi salt and 9.8% MWCNT composite gave the typical two reduction peaks and two oxidation peaks; these are due to three polysulfide species. The initial discharge capacity was 1334.4 mAh g–1-S for the PANi-S/MWCNT electrode and the remaining capacity was 932.4 mAh g–1-S after 80 cycles. The columbic efficiency doubled to 92.4% compared to S-MWCNT-2. The rate of the reaction upon using PANi-S/MWCNT electrode was found to be almost twice that of the S/MWCNT composites. Because of the porous polymer, the diffusion distance of the lithium ion from the bulk liquid was reduced. The gel-like cathode composites and the higher conductivities improved the kinetics of the lithium sulfur redox reaction.