Sulfur-based electrode using a polyelectrolyte binder via coupled in situ synchrotron X-ray diffraction and tomography

Polyelectrolytes are promising binders for sulfur cathodes of Li/S batteries, with an ability to control the diffusion of polysulfides into the electrolyte, but their impact on the microstructural evolution of the electrode with cycling is presently unknown. In this study, coupled in situ synchrotron X-ray diffraction and tomography analyses are performed during the 1st and 11th cycles of a sulfur-based electrode made with poly(diallyldimethylammonium) bis(trifluoromethane sulfonyl)imide as a polyelectrolyte binder. Sulfur deposited at the end of the 1st charge is mainly β-S₈, but some α-S₈ is also deposited during the 1st charge on the unreacted α-S₈ particles. No α-S₈ is detected at the 11th cycle, suggesting that the remaining α-S₈ reacts progressively with cycling. The carbon-binder domain is not discernible due to spatial and contrast resolution limitations, and thus, its evolution with cycling and its specific role on the sulfur dissolution and deposition processes cannot be clearly established. However, the fact that there is no collapsing of the electrode in the sulfur-depleted zones (in contrast to what was observed in the literature with a conventional binder such as poly(vinylidene difluoride) (PVdF)) suggests that the present polyelectrolyte is an efficient binder to preserve the electrode architecture upon cycling.
doi.org/10.1021/acsaem.9b02108