Polypyrrole Modification of High Sulfur-Loaded Three-Dimensional Aluminum Foam Cathode in Lithium-Sulfur Batteries for High-Rate Capability

A low-resistance polypyrrole (PPy) film that can achieve high rates (rates of >1C) while suppressing polysulfide dissolution is developed in this study. To achieve high-rate characteristic in a sulfur cathode with high sulfur loading, a three-dimensional (3D) aluminum foam current collector is used and the Li+ concentration of the PPy film is enhanced by a glyme-Li equimolar complex as the polymerization electrolyte. A PPy-sulfur/ketjenblack (S/KB) 3D aluminum foam laminated cell with a sulfur loading of 5 mg cm-2 is prepared. Consequently, a high discharge capacity of 794 mAh g-1-sulfur at 3.0C is achieved using 1 M lithium bis-(trifluoromethylsulfonyl)imide (LiTFSI) with dimethoxyethane (DME) and 1,3-dioxolane (DOL), (DME/DOL = 1/1 vol.) as the electrolyte and Li foil as the anode. In the cycling test, PPy-S/KB 3D Al foam cathode achieved a significant improvement in discharge capacity retention compared to bare S/KB 3D Al foam cathode without PPy coating. Moreover, almost no polysulfide dissolution is confirmed from the ultraviolet-visible spectrum of the electrolyte after the cycle evaluation. Here, we prepare a 3D structure S/KB cathode that can support high rates while suppressing sulfur dissolution by PPy coating, and reveal its potential for lithium-sulfur battery application.