Binder Based on Polyelectrolyte for High Capacity Density Lithium/Sulfur Battery

Lithium/sulfur (Li/S) battery is unique in that it is indeed a liquid electrochemical system. In discharge, elemental sulfur is first reduced into high order polysulfide (PS, Li 2 S x , x = 8), which dissolves into liquid electrolyte and leaves voids in the cathode, whereas in the last stage, the dissolved low order PS (Li 2 S x , x = 4) is reduced into insoluble Li 2 S 2 and Li 2 S, which fill the voids up. In order to facilitate reversible cycling, the sulfur cathode is required to be capable of retaining the stable void structure. For this purpose, we introduce a poly(acrylamide-co-diallyldimethylammonium chloride) (AMAC) as the binder of high sulfur loading cathodes. AMAC is a cationic polyelectrolyte, which is substantially insoluble in organic solvent while being highly soluble in water. This feature enables the cathode to retain the stable void structure formed repeatedly during discharge and charge cycling of the sulfur cathode. However, in the process of aqueous slurry coating, AMAC causes severe pitting corrosion of Al current collector. In this work, we study AMAC binder by comparing it with the conventional poly(ethylene oxide) (PEO) binder, discussing the mechanism of Al pitting corrosion, and finally solving the problem of Al corrosion.