We report here a water-based functional binder framework for the lithium-sulfur battery systems, based on the general combination of a polyether and an amide-containing polymer. These binders are applied to positive electrodes optimised towards high-energy electrochemical performance based only on commercially available materials. Electrodes with up to 4 mAh cm capacity and 97-98 % coulombic efficiency are achievable in electrodes with a 65 % total sulfur content and a poly(ethylene oxide):poly(vinylpyrrolidone) (PEO:PVP) binder system. Exchange of either binder component for a different polymer with similar functionality preserves the high capacity and coulombic efficiency. The improvement in coulombic efficiency from the inclusion of the coordinating amide group was also observed in electrodes where pyrrolidone moieties were covalently grafted to the carbon black, indicating the role of this functionality in facilitating polysulfide adsorption to the electrode surface. The mechanical properties of the electrodes appear not to significantly influence sulfur utilisation or coulombic efficiency in the short term but rather determine retention of these properties over extended cycling. These results demonstrate the robustness of this very straightforward approach, as well as the considerable scope for designing binder materials with targeted properties.

The lithium-sulfur (Li-S) battery has seen a resurgence of interest in recent years, with hundreds of journal articles now published every year. Significant advances have been made towards tackling the long-standing issues of poor efficiency and cycle life, most of which derive from the well-known polysulfide redox shuttle. Optimisation of the structure of the positive electrode, to improve contact to insulating solid particles and control the diffusion of soluble intermediates, has been one of the most intensely explored areas within this field. However, much of the published research involves increasingly exotic materials synthesis techniques which may not prove suitable when scaled up to the order of tons, which would be required if the system is to break into consumer applications. Our group has previously investigated the use of functional polymers for use as binders in this system, particularly polyethers, such as PEO, and amide/lactam-containing polymers such as PVP. These water-soluble commodity polymers can actively improve active material utilisation, efficiency, and rate capability, depending on the materials chosen. Recently, we have investigated the compatibility of these materials with commercially available carbon materials suited towards electrodes with higher energy densities (e.g., highly porous carbon blacks). In this way, electrodes have been prepared from water-based processes with sulfur loadings of 65% and higher and areal capacities up to 4 mAh/cm2, with reversible sulfur utilisations in excess of 1000 mAh/g. Such figures are among the highest reported for this system. This presentation will summarise our work in optimising positive electrodes based on porous carbon blacks and functional binders. New results on previously unreported materials will also be presented, as well as the results of electrochemical characterisation of cells employing these electrodes where other cell components have been further optimised towards high-energy: particularly the electrolyte volume and the excess of the lithium-metal anode.