The enhancing effects of polyaniline (PANi) coatings on ion and electron conductivity are well known (see also here), which is why researchers from the Sun Yat-sen University (China) devised PANi-coated activated carbon/sulfur aerogels (ACA-500-S) in order to improve the electrochemical properties of the un-coated composite. By synthesizing this novel electrode material, the research team hopes to address drawbacks of Li-S batteries (e.g. low ionic conductivity, dissolution of polysulfides in electrolytes).
Carbon/sulfur composite aerogels were produced by heat-melting state-of-the-art activated carbon aerogels (ACA-500) in the presence of elemental sulfur. As shown in the Figure below, the PANi coating was subsequently applied by in-situ chemical oxidative polymerization at low temperatures, yielding the final ACA-500-S@PANi electrode material. Investigation of the sample morphology via FESEM and TEM revealed that the manufacturing technique led to a homogeneous distribution of sulfur and PANi on the aerogel surface. Because of the even dispersion of the active agents on the aerogel matrix, enhanced electrochemical performance was expected from the ACA-500-S@PANi composite.
This expectation was confirmed in ensuing experiments, which compared the specific capacity, capacity discharge, and capacity retention of the ACA-500-S and ACA-500-S@PANi materials. It was shown that the latter material outperformed the carbon/sulfur aerogel in all regards, which was attributed to the synergistic effect of the carbon aerogel matrix and the PANi coating on ion and electron conductivity as well as electrode stability. More specifically, the researchers discovered that the ACA-500-S@PANi structure presented high reversible capacities at low (at 0.2 C: 1208 mAh g−1) and high (at 3.0 C: 542 mAh g−1) discharge rates. Furthermore, long term cycling at 1.0 C demonstrated that it exhibits a notable initial discharge capacity of 926 mAh g-1 and outstanding capacity retention of over 65 % at a low capacity decay rate of 0.48 ‰ per cycle.
Because of these findings, the researchers are confident that the novel aerogel composite will be able to boost the performance of lithium-sulfur batteries, meeting the increasing demand for batteries exhibiting a high energy density and long life span at low cost.
More details: Tang et al.; Polyaniline-Coated Activated Carbon Aerogel/Sulfur Composite for High- performance Lithium-Sulfur Battery, Nanoscale Research Letters 2017. https://doi.org/10.1186/s11671-017-2372-6
