Hierarchical sulfur confinement by graphene oxide wrapped, walnut-like carbon spheres for cathode of Li-S battery

Abstract

Inadequate cycle stability is a major issue hindering practical application of lithium sulfur (Li-S) batteries. We herein report a graphene oxide wrapped, multi-cavity, walnut-like carbon sphere (GO-MCWCS) cathode which may help to alleviate the above issue. The multi-cavity, walnut-like carbon spheres were obtained through a templated sol-gel process. Sulfur and polysulfides (the discharge intermediate at the cathode) are effectively immobilized in the GO-MCWCS cathode through a hierarchical mode of confinement, i.e. multiple levels of physical confinement by the abundant cavities of the walnut-like structure and the graphene oxide wrapping layer. The functional groups on GO (such as epoxy and hydroxyl groups) also help to retain polysulfides in the cathode via chemical binding. Attributed to the rational design of the GO-MCWCS cathode, our Li-S battery displayed an excellent cycle performance (85% capacity retention and nearly 100% coulombic efficiency after 200 cycles at 0.5C) and a good rate capability (905 mAh g−1 and 680 mAh g−1 at 1C and 2C, respectively). It is believed that the novel GO-MCWCS composite structure is a promising cathode design for advanced Li-S batteries.