Porous carbons have been widely used as host materials for sulfur (S) electrodes because of their high conductivity and high surface area. But they generally lack strong chemical affinity to bind and stabilize various soluble polysulphide species. They frequently are doped by heteroatoms or coated with inorganic nanoparticles. Conducting polymers such as polyaniline (PANi), Polypyrrole (PPY) and poly(3,4-ethylenedioxythiophene) (PEDOT) have shown the capability to stabilize nanostructured S electrodes due to the existence of strong polysulphide-binding groups and their good conductivity from electrochemical doping. Integrating conducting polymer with high-surface-area carbons can create a new materials platform for S electrodes that synergize their functions. However, those conducting polymers are often insoluble and coating them uniformly from solution onto non-polar carbon substrate is a challenge. Here, we report that solution processable isoindigo-based conjugated polymers incorporating polar substituents (pyridine derivatives) inside the backbone and sidechains provide critical features for making hybrid sulfur electrode: 1) conjugated backbone provide high conductivity. 2) functional pyridine and amide groups in the polymer backbone and side-chains provide high affinity to LixS and 3) high solubility to organic solvents. Their utilization leads to effective coating to provide highly stable sulfur electrodes. This polymer enabled us to develop a general coating approach to different kinds of carbonaceous materials. Importantly, with this efficient hybrid structure, the electrodes exhibit high capacity retention (80 % over 300 cycles) in high sulfur mass loading (3.2 mg/cm2) and with high sulfur content of 90 %, which have never been achieved before in polymer-enabled sulfur cathodes.

Enhanced cycling stability of  sulfur electrodes through effective binding of pyridine-functionalized conjugated polymer

254th National Meeting (2017)

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