Regulating Polysulfide Redox Kinetics on a Self-Healing Electrode for High-Performance Flexible Lithium-Sulfur Batteries

Wearable electronics require lightweight and flexible batteries, of which lithium-sulfur (Li-S) batteries are of great interest due to their high gravimetric energy density. Nevertheless, flexible Li-S batteries have unsatisfactory electrochemical performance owing to electrode fracture during repeated bending, the volume change of sulfur species and the severe shuttle effect. Binders play essential roles in these batteries but have always lacked attention. Herein, a self-healing polyvinylpyrrolidone-polyethyleneimine (PVP-PEI) binder cross-linked by hydrogen bonds, which also regulates polysulfide redox kinetics, is reported. The dynamic hydrogen-bonding networks repair the cracks and ensure the integrity of the electrode while numerous polar groups such as C(sic)O and -NH2 suppress the shuttle effect by immobilizing polysulfides. Therefore, Li-S batteries with the PVP-PEI binder exhibit excellent cycling stability (a capacity decay rate of 0.0718% per cycle at 1 C after 450 cycles), an outstanding areal capacity of 7.67 mAh cm(-2) even under a high sulfur loading (7.1 mg cm(-2)) and relatively lean electrolyte conditions (E/S ratio = 8 mu L mg(-1)). Flexible Li-S pouch cells using the PVP-PEI binder show a stable performance for 140 cycles and a favorable capacity retention of over 95% after 2800 bending cycles, confirming its application potential in high-performance flexible Li-S batteries.

Automated summary

The flexible Li-S batteries using the PVP-PEI binder exhibit excellent cycling stability and high areal capacity, showing great potential for high-performance wearable electronics. The self-healing PVP-PEI binder, cross-linked by hydrogen bonds, plays a key role in improving the battery's performance and stability.