Cost-Effective Water-Soluble Poly(vinyl alcohol) as a Functional Binder for High-Sulfur-Loading Cathodes in Lithium-Sulfur Batteries.

Binder, as one of the key components, plays a crucial role in improving the capacity and cycling performance of lithium-sulfur (Li-S) batteries. In this work, commercially available, low-cost, water-soluble polyvinyl alcohol (PVA) has been systematically investigated as a functional polymer binder for high-sulfur-loading cathodes, with the aim of enhancing sulfur utilization, reducing capacity decay, and extending cycling life of the cathodes. In comparison with polyvinylidene fluoride as a conventional binder, PVA shows a valuable polysulfide entrapping ability and a much stronger binding strength. Its superior polysulfide entrapping ability has been verified through theoretical density functional theory calculations and an experimental adsorption study. In electrochemical Li-S battery performance evaluation, at a sulfur loading density of 3.5 mg cm, the sulfur cathode assembled with the PVA binder displays at 0.5 C a very slow capacity decay of only 0.010% per cycle over 250 cycles. Additionally, the strong binding strength of PVA allows the fabrication of thick sulfur cathodes with a high sulfur loading density of 10.5 mg cm, which shows a high areal capacity of 4.0 mA h cm and a high cycling stability (capacity decay of 0.1% per cycle). In consideration of the superior capacity retention and cycling performance of its enabled cathodes, the cost-effective PVA is a promising candidate for high-sulfur-loading cathodes in practical applications.