Zhangxiang Hao

TiN as a simple and efficient polysulfide immobilizer for lithium–sulfur batteries

Lithium–sulfur batteries are believed to be potential next-generation electrochemical devices which will satisfy the increasing market demands due to their high energy density, low cost and environmental friendliness. However, the practical application of Li–S batteries is still hindered by poor cycle stability and rate capability caused by the low electronic conductivity of sulfur and dissolution of intermediate polysulfides. Here, we employ easily-obtained titanium nitride (TiN) as a highly efficient immobilizer to trap polysulfides via a chemical mechanism. TiN also possesses high electronic conductivity which helps in achieving a high sulfur utility and an excellent rate capability. At 0.5C, the TiN-based sulfur composite cathode demonstrates a high initial reversible capacity of 1012 mA h g−1 and a long cycle life of over 200 cycles with a decay rate of 0.2% per cycle. Even at 5C, the reversible discharge capacity is still higher than 550 mA h g−1. The outstanding electrochemical performance is ascribed to the strong chemisorption effect between TiN and polysulfides.

Coordination of Surface-Induced Reaction and Intercalation: Toward a High-Performance Carbon Anode for Sodium-Ion Batteries

Oxygen‐rich carbon material is successfully fabricated from a porous carbon and evaluated as anode for sodium‐ion battery. With the strategy of optimal combination of fast surface redox reaction and reversible intercalation, the oxygen‐rich carbon anode exhibits a large reversible capacity (447 mAh g−1 at 0.2 A g−1), high rate capability (172 mAh g−1 at 20 A g−1), and excellent cycling stability.

Free-Standing Mn3O4@CNF/S Paper Cathodes with High Sulfur Loading for Lithium–Sulfur Batteries

Free-standing paper cathodes with layer-by-layer structure are synthesized for high-loading lithium-sulfur (Li-S) battery. Sulfur is loaded in a three-dimensional (3D) interconnected nitrogen-doped carbon nanofiber (CNF) framework impregnated with Mn3O4 nanoparticles. The 3D interconnected CNF framework creates an architecture with outstanding mechanical properties. Synergetic effects generated from physical and chemical entrapment could effectively suppress the dissolution and diffusion of the polysulfides. Electrochemical measurements suggest that the rationally designed structure endows the electrode with high utilization of sulfur and good cycle performance. Specifically, the cathode with a high areal sulfur loading of 11 mg cm-2 exhibits a reversible areal capacity over 8 mAh cm-2. The fabrication procedure is of low cost and readily scalable. We believe that this work will provide a promising choice for potential practical applications.

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

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.