Polycation Binders: An Effective Approach toward Lithium Polysulfide Sequestration in Li–S Batteries

Lithium polysulfide sequestration by polymeric binders in lithium–sulfur battery cathodes is investigated in this study. We prove polycations can effectively adsorb lithium polysulfides via Coulombic attraction between the positively charged backbone and the polysulfide anions. For the first time, we measure the simultaneous mass change of the sulfur cathodes with poly(diallyldimethylammonium triflate) (PDAT) and polyvinylpyrrolidone (PVP) binders during lithiation–delithiation using electrochemical quartz crystal microbalance (EQCM). The EQCM results demonstrate significantly higher mass gain with PDAT binder under identical conditions, providing direct evidence that PDAT is a superior binder. The advantage of polycation binders is also proved by charge–discharge cycling combined with ultraviolet–visible spectroscopy and X-ray photoelectron spectroscopy. With the PDAT binder and minimized electrolyte/sulfur weight ratio, we further demonstrate electrodes with high sulfur loading achieving 4.2 mAh cm –2 areal capacity.