Integrated graphene-sulfur cathode and separator with plasma enhancement for Li-S batteries

Lithium-sulfur (Li-S) battery has been extensively studied due to its high theoretical energy density. Carbon materials have been developed as conductive scaffolds to improve the electrical conductivity of sulfur, and as a coating layer of the separator to restrain the shuttling effect of polysulfide. However, previous designs of the Li-S battery lack a good adhesion between the cathode and the separator, thus motivating further research on design and materials selection to achieve the optimal battery performance. Herein, the free-standing oxygen plasma functionalized three-dimensional graphene-sulfur (O3DG-S)/polypropylene (OPP) separator composite introduces for the first-time, tri-functional structure (TFS) in a Li-S battery: a current collector, cathode material and a part of the separator. The O3DG exhibited a moderate electrical conductivity, with very good mechanical integrity, making it a promising candidate as a flexible current collector, as well as a scaffold for sulfur. The unique surface morphology of O3DG-S treated by oxygen plasma functionalization for promoting a seamless contact with commercial PP separator for a "Janus type" multifunctional separator structure. The TFS showed a capacity of ∼1400 mAh g−1 at 0.1 C with a sulfur loading of ∼70 wt% and a high cyclic performance of Li-S battery.