Impact of the binder nature on the morphological change of sulfur electrodes upon cycling investigated by in situ characterization methods

Abstract

The binder used in the formulation of sulfur electrodes for Li/S batteries plays a crucial role in their electrochemical performance. In the present study, the impact of using a polyelectrolyte binder (poly(diallyldimethylammonium) bis(trifluromethane sulfonyl)imide) on the morphological degradation of sulfur electrodes is evaluated by in situ dilatometry, acoustic emission (AE) and synchrotron X-ray tomography (XRT), and compared to more conventional binders (poly(vinylidene difluoride) (PVdF) and carboxymethylcellulose (CMC)). The dilatometry study shows that during the initial sulfur dissolution process, the polyelectrolyte-based electrode displays a lower irreversible thickness contraction of ~16% compared to ~22% and ~31% for CMC and PVdF, respectively. This is confirmed by the XRT measurements showing a reduced thickness variation for the polyelectrolyte electrode compared to the CMC electrode. The same trend is found in the AE results, where a lower acoustic activity attributed to the rupture of the binder/carbon/sulfur network is detected during the 1st discharge plateau for the polyelectrolyte electrode. All these results confirm the major role of the binder for the Li/S system. Thanks to its multifunctionality, it impacts both the diffusion of the active material outside the electrode and the electrode integrity and therefore the conduction paths and accessible active surface for electrochemical processes.