Electro-polymerized polypyrrole film for fabrication of flexible and slurry-free polypyrrole-sulfur-polypyrrole sandwich electrode for the lithium-sulfur battery

Thin films of polypyrrole (PPy) were electrochemically synthesized from direct oxidation of pyrrole (Py) which is a five-membered ring heterocyclic aromatic compound with a dipole moment of 1.58D. The electro-polymerized PPy thin film shows sufficiently good mechanical properties to be included in a self-supporting free-standing layered cathode. Physical and morphological characterizations show that this PPy film is flexible, robust, lightweight, corrugated, and highly conductive. These properties facilitate the use of PPy thin film in a self-supported flexible electrode composed of slurry-free PPy-sulfur-PPy sandwiched structure. Because the conventional slurry casting method could be avoided, a large amount of active material could be loaded in between the corrugated PPy films. The newly developed flexible PPy-sulfur-PPy sandwiched electrode thus show high capacity when coupled with lithium, along with good cycling performance and excellent capacity retention.