Biomimetic Root-like TiN/C@S Nanofiber as a Freestanding Cathode with High Sulfur Loading for Lithium-Sulfur Batteries.

ABSTRACT

It is a tough issue to achieve high electrochemical performance and high sulfur loading simultaneously, which is of important significance for practical Li-S batteries applications. Inspired by the transportation system of the plant root in nature, a biomimetic root-like carbon/titanium nitride (TiN/C) composite nanofiber is designed as a freestanding current collector for the high sulfur loading cathode. Like the plant root which absorbs water and oxygen from soil and transfers them to the trunk and branches, the root-like TiN/C matrix provides high-efficiency polysulfide, electron, and electrolyte transfer for the redox reactions via its three-dimensional-porous interconnected structure. In the meantime, TiN can not only anchor the polysulfides via the polar Ti-S and N-S bond but also further facilitate the redox reaction because of its high catalytic effect. With 4 mg cm-2 sulfur loading, the TiN/C@S cathode delivers a high initial discharge capacity of 983 mA h g-1 at 0.2 C current density; after 300 charge/discharge cycles, the discharge capacity remains 685 mA h g-1, corresponding to a capacity decay rate of ∼0.1%. Even when the sulfur loading is increased to 10.5 mg cm-2, the cell still delivers a high capacity of 790 mA h g-1 and a decent cycle life. We believe that this novel biomimetic root-like structure can provide some inspiration for the rational structure design of the high-energy lithium-sulfur batteries and other composite electrode materials.