Sulfur-polyaniline coated mesoporous carbon composite in combination with carbon nanotubes interlayer as a superior cathode assembly for high capacity lithium-sulfur cells

摘要

Lithium-sulfur (Li-S) cells are gaining upper hand as the next generation energy storage systems with remarkable electrochemical features, suitable for applications in portable electronic devices and hybrid electric vehicles. The present work is focused on analyzing the effects of the polyaniline coated mesoporous carbon used for modifying the sulfur cathode and the flexible interlayer of carbon nanotubes (CNT interlayer), inserted between the cathode and the separator, on the electrochemical performance of the assembled Li-S cells. The composite of sulfur with the polyaniline (PANI) coated mesoporous carbon (SPMC) is used as the modified cathode material. The PANI coated mesoporous carbon (PMC) synthesized by in situ polymerization is subjected to solvothermal treatment with sulfur to obtain the SPMC cathode. The cells assembled using the SPMC composite as cathode with a sulfur content of 80 wt% and CNT film as interlayer exhibit an initial discharge capacity of 1137 mAhg(-1) at 0.2 C rate. Furthermore, at 1 C rate the cells deliver a discharge capacity of 968mAhg(-1) at the initial cycle and 700mAhg(-1) after 200 cycles corresponding to an extremely low capacity decay of 0.14% per cycle. The highly conducting polyaniline coated carbon helps in enhancing the electrical contact of the modified cathode and thus limits the dissolution of the lithium polysulfides and the associated shuttling effect during cycling. The polyaniline encapsulation can also minimize the adverse effects of the volume expansion of sulfur during lithium intake. The porous structured CNT interlayer contributes towards enhancing the overall electrical conductivity of the cathode assembly and localizes the migrating polysulfides within the cathode region, which helps to further hinder the polysulfide shuttling phenomenon. The novelty of the work is in the effective modification of the sulfur cathode using the cost-effective, electrically conducting and eco-friendly polyaniline and mesoporous carbon to achieve the required electrical contact, good control over the volume expansion of sulfur during lithium intake and better utilization of sulfur. The modifications effected on the sulfur cathode by the presence of the polyaniline coated carbon, along with the role of the CNT interlayer in meticulously controlling the polysulfide shuttle phenomenon substantially contribute towards improving the capacity and the cycling stability of the assembled Li-S cells.