Jingwei Xiang

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.

3D interconnected porous NiMoO4 nanoplate arrays on Ni foam as high-performance binder-free electrode for supercapacitors

3D interconnected NiMoO4 nanoplate arrays (NPAs) are grown on Ni foam (NPAs@Ni) via a facile hydrothermal reaction. The obtained NPAs@Ni is directly used as a binder-free integrated electrode for supercapacitors. The optimized electrode exhibits a specific capacitance as high as 3.4 F cm−2 (2138 F g−1) at a current density of 2 mA cm−2, and an excellent cyclability with 87% retention of the initial specific capacitance after 3000 cycles. The remarkable electrochemical performance can be attributed to the interconnected architecture in which the electrons and ions readily transport along the conductive 3D channels.

Granadilla-Inspired Structure Design for Conversion/Alloy-Reaction Electrode with Integrated Lithium Storage Behaviors

Conversion/alloy-reaction electrode materials promise much higher energy density than the commonly used ones based on intercalation chemistries. However, the low electronic conductivity and, specially, the large volume expansion upon lithiation hinder their practical applications. Here, for the first time, a unique granadilla-inspired structure was designed to prepare the conversion/alloy-reaction anode of carbon coated tin/calcium tin oxide (C@void@Sn/CaSnO3) ternary composite. The granadilla-inspired structure ensures the intimate contact between the Sn/CaSnO3 nanoparticles and the carbon matrix, providing not only conductive networks for electron transport and a short distance for Li+ diffusion but also effective space for the electrode volume expansion toward conversion/alloy reaction. Moreover, the unique structure possesses abundant solid-solid interfaces between the three components as well as solid-liquid interfaces between nanoparticles and electrolyte, contributing to a large percent (58%) of interfacial charge (thus capacity). The integration of alloy-reaction, conversion-reaction, and interfacial lithium storage endows the hybrid electrode with a high capacity and long cycling life, holding great promise for next-generation high-capacity lithium-ion batteries.

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.

A separator-based lithium polysulfide recirculator for high-loading and high-performance Li–S batteries

Lithium–sulfur (Li–S) batteries are promising for the next-generation energy storage devices due to their high theoretical energy density and low cost. However, the shuttle effect and the passive layer between the separator and electrode still affect the cycling stability and coulombic efficiency seriously. Herein, we develop a 10 μm-thick rGO (reduced graphene oxide) and molybdenum phosphide (MoP) composite coating layer on a Celgard separator to improve the electrochemical performance of Li–S batteries. The introduction of such a MoP/rGO coating layer on the separator not only impedes the diffusion of polysulfides to the anode but also improves the sulfur utilization. In particular, the 10 nm MoP nanoparticles are very efficient for the polysulfide adsorption. Compared to the pristine Celgard separator, superior electrochemical performance is obtained in both coin cells and pouch cells with the MoP/rGO coated separator. High areal capacity (∼3 mA h cm−2), good rate performance, and long cycle life (300 cycles) are attained under a sulfur loading of 3.88 mg cm−2. The capacity decay rate is as low as 0.045% per cycle over 300 cycles. In addition, the pouch cells made by the modified separator with a high sulfur loading of 4.6 mg cm−2 achieve good electrochemical performance. At 0.1C, the initial discharge capacity is 1083 mA h g−1, and still remains at 759 mA h g−1 after 120 cycles. The result reveals the potential practical use of this MoP/rGO coated separator for Li–S batteries.

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.