Toward a Better Understanding of the Surface Effect through the Design of Conductive Binders in Lithium Sulfur Battery

Li-S battery has attracted much attention, because of the extreme high theoretical capacity and low cost compare to Li-ion battery. But the poor cycling life of lithium sulfur battery kept them from large scale usage. The poor electric conductivity of the charge and discharge product is another limitation for Li-S battery. A lot of research work has focused on the improvement of electrode design, including the combination of porous carbon film, carbon paper, carbon nanotube, graphene or other conductive nanostructure. The design of binder is another effect way to improved the battery performance, because the binder covers up most of the inner surface of the electrode, which has a important effect in surface modification. In Li-S battery, a notable feature of phase transformation will take place, which are from solid phase S₈/Li₂S₈ into soluble Li2S4, then precipitate into solid state Li2S during discharge and the combination of solid phase and liquid phase reaction during charge. The surface effect of binder will have a much bigger influence on Li-S battery performance because this phase transformation.

So in this work, we investigated several binders with different kind of functional group, including both conductive and nonconductive binders, to study the effect of binder on surface modification. A huge difference is observed in electrochemical performance and electrode morphology with different binders. These indicates the different effect of binder on surface modification and therefore in reaction mechanism during charge and discharge. So, we suggest that the designing of binder with preferred physical and electrochemical property in indeed crucial in further improving the performance of Li-S battery.