Synergistic Cation-Anion Regulation of Polysulfides by Zwitterionic Polymer Binder for Lithium-Sulfur Batteries

The practical application of lithium-sulfur (Li-S) batteries is gravely hampered by the dissolution and shuttle of lithium polysulfides. Herein, a zwitterionic polymer binder with both lithiophilicity and sulfophilicity is skillfully designed to realize a synergistic regulation of cations and anions through the strong interactions with lithium polysulfides. The cationic quaternary ammonium group within the polymeric zwitterion can immobilize polysulfide anions and block polysulfide migration, while the sulfonate anions preferably couple with lithium ion, thus facilitating ion transfer and promoting the polysulfides redox kinetics. The dynamic networks crosslinked by both hydrogen bonding and electrostatic interaction enable mechanically robust cathodes to withstand the volume variation and spontaneously repair cracks upon repeated lithiation/delithiation. Benefiting from these attributes, the Li-S coin cell using the zwitterionic polymer binder delivers a high initial discharge capacity of 1230.6 mAh g(-1) at 0.2 C as well as an ultralow capacity decay rate of 0.03% per cycle over 600 cycles at 2 C. In Li-S pouch cell level, a high areal capacity of 6.6 mAh cm(-2) after 50 cycles can be obtained under a sulfur loading of up to 8.5 mg cm(-2), demonstrating the potential of zwitterionic polymer binder for the further development of high-performance Li-S batteries.

Automated summary

A zwitterionic polymer binder with lithiophilicity and sulfophilicity is designed to regulate cations and anions in lithium-sulfur batteries. The binder immobilizes polysulfide anions and couples with lithium ions, facilitating ion transfer and promoting redox kinetics. The binder also enables mechanically robust cathodes that can withstand volume variation and repair cracks. The Li-S battery using the binder delivers high initial discharge capacity and low capacity decay rate.