Imparting Pulley Effect and Self-healability to Cathode Binder of Li-S Battery for Improvement of the Cycling Stability

To construct structurally stable sulfur cathode of Li-S battery with improved cycling performance, poly(acrylic acid) (PAA) crosslinked by cationic hydroxypropyl polyrotaxane (HPRN + ) via dynamically reversible boronic ester bonds is synthesized and serves as the cathode binder. The smart polymer networks offer multifunction including buffering the volume change of the cathode during charge/discharge through the pulley effect of polyrotaxanes (PR), suppressing the shuttle effect by adsorption of polysulfide using the plentiful carboxyl, hydroxyl and quaternary ammonium cationic groups, and self-healing the micro-damages to ensure stable conduction pathways of the electrode. As a result, the Li-S batteries based on this novel multifunctional binder and simple commercial sulfur/carbon composites cathode exhibit excellent specific capacity and cycling stability. In particular, the specific capacity decay per cycle of the cell is only 0.064% along with high Coulombic efficiency after 550 cycles at 1.0 C, which is superior to most of the reported binders. Even under high sulfur loading, moreover, the cathode can deliver superior areal capacity and cycling stability. This proposed binder provides a new way for the design of high-stability sulfur cathodes.