Yanfeng Dong

Enhancing lithium–sulphur battery performance by strongly binding the discharge products on amino-functionalized reduced graphene oxide

Lithium-sulphur batteries are one very appealing power source with high energy density. But their practical use is still hindered by several issues including short lifespan, low efficiency and safety concern from the lithium anode. Polysulphide dissolution and insulating nature of sulphur are generally considered responsible for the capacity degradation. However, the detachment of discharge products, that is, highly polar lithium sulphides, from nonpolar carbon matrix (for example, graphene) has been rarely studied as one critical factor. Here we report the strongly covalent stabilization of sulphur and its discharge products on amino-functionalized reduced graphene oxide that enables stable capacity retention of 80% for 350 cycles with high capacities and excellent high-rate response up to 4 C. The present study demonstrates a feasible and effective strategy to solve the long-term cycling difficulty for lithium-sulphur batteries and also helps to understand the capacity decay mechanism involved.

Low temperature plasma synthesis of mesoporous Fe3O4 nanorods grafted on reduced graphene oxide for high performance lithium storage.

Transition metal oxide coupling with carbon is an effective method for improving electrical conductivity of battery electrodes and avoiding the degradation of their lithium storage capability due to large volume expansion/contraction and severe particle aggregation during the lithium insertion and desertion process. In our present work, we develop an effective approach to fabricate the nanocomposites of porous rod-shaped Fe3O4 anchored on reduced graphene oxide (Fe3O4/rGO) by controlling the in situ nucleation and growth of β-FeOOH onto the graphene oxide (β-FeOOH/GO) and followed by dielectric barrier discharge (DBD) hydrogen plasma treatment. Such well-designed hierarchical nanostructures are beneficial for maximum utilization of electrochemically active matter in lithium ion batteries and display superior Li uptake with high reversible capacity, good rate capability, and excellent stability, maintaining 890 mA h g(-1) capacity over 100 cycles at a current density of 500 mA g(-1).

Dually Fixed SnO2 Nanoparticles on Graphene Nanosheets by Polyaniline Coating for Superior Lithium Storage

Dually fixed SnO2 nanoparticles (DF-SnO2 NPs) on graphene nanosheets by a polyaniline (Pani) coating was successfully fabricated via two facile wet chemistry processes, including anchoring SnO2 NPs onto graphene nanosheets via reducing graphene oxide by Sn(2+) ion, followed by in situ surface sealing with the Pani coating. Such a configuration is very appealing anode materials in LIBs due to several structural merits: (1) it prevents the aggregation of SnO2 NPs, (2) accommodates the structural expanding of SnO2 NPs during lithiation, (3) ensures the stable as-formed solid electrolyte interface films, and (4) effectively enhances the electronic conductivity of the overall electrode. Therefore, the final DF-SnO2 anode exhibits stable cycle performance, such as a high capacity retention of over 90% for 400 cycles at a current density of 200 mA g(-1) and a long cycle life up to 700 times at a higher current density of 1000 mA g(-1).

Nitrogen-doped graphene nanoribbons for high-performance lithium ion batteries

Nitrogen-doped graphene nanoribbons (N-GNRs) were synthesized through longitudinal unzipping of nitrogen-doped carbon nanotubes filled with iron nanowires (Fe@CNx-CNTs) by means of nitric acid oxidation. Benefiting from their N doping and edge effect, N-GNRs showed high capacity, excellent cycling performance and rate capability as anode materials in lithium ion batteries (LIBs).

Flexible Paper-like Free-Standing Electrodes by Anchoring Ultrafine SnS2 Nanocrystals on Graphene Nanoribbons for High-Performance Sodium Ion Batteries

Ultrafine SnS2 nanocrystals-reduced graphene oxide nanoribbon paper (SnS2-RGONRP) has been created by a well-designed process including in situ reduction, evaporation-induced self-assembly, and sulfuration. The as-formed SnS2 nanocrystals possess an average diameter of 2.3 nm and disperse on the surface of RGONRs uniformly. The strong capillary force formed during evaporation leads to a compact assembly of RGONRs to give a flexible paper structure with a high density of 0.94 g cm-3. The as-prepared SnS2-RGONRP composite could be directly used as free-standing electrode for sodium ion batteries. Due to the synergistic effects between the ultrafine SnS2 nanocrystals and the conductive, tightly connected RGONR networks, the composite paper electrode exhibits excellent electrochemical performance. A high volumetric capacity of 508-244 mAh cm-3 was obtained at current densities in the range of 0.1-10 A g-1. Discharge capacities of 334 and 255 mAh cm-3 were still kept, even after 1500 cycles tested at current densities of 1 and 5 A g-1, respectively. This strategy provides insight into a new pathway for the creation of free-standing composite electrodes used in the energy storage and conversion.

Towards efficient electrocatalysts for oxygen reduction by doping cobalt into graphene-supported graphitic carbon nitride

A highly efficient electrocatalyst is developed by chemical coordination of cobalt species with g-C3N4 layers which are homogeneously supported on reduced graphene oxide. The formation of Co-Nx complex active sites greatly enhances the electrocatalytic activity and durability towards the oxygen reduction reaction.

Self-assembled sulfur/reduced graphene oxide nanoribbon paper as a free-standing electrode for high performance lithium–sulfur batteries

Flexible, interconnected sulfur/reduced graphene oxide nanoribbon paper (S/RGONRP) is synthesized through S2- reduction and evaporation induced self-assembly processes. The in situ formed sulfur atoms chemically bonded with the surface of reduced graphene oxide nanoribbons and were physically trapped by the compact assembly, which make the hybrid a suitable cathode material for lithium-sulfur batteries.

Tailor-made graphene aerogels with inbuilt baffle plates by charge-induced template-directed assembly for high-performance Li–S batteries

Graphene as a host material has attracted intense interest to accommodate the sulfur for lithium–sulfur (Li–S) batteries. Nevertheless, there is still a major challenge on how to modulate the nanostructure of graphene architectures to further enhance the electrochemical performance. Herein, self-closure graphene aerogels with inbuilt baffle plates (SGA) were prepared by a combined strategy involving electrostatic assembly, hydrothermal fixing, polydopamine (PDA) coating, and annealing. The electrostatic assembly between graphene oxide (GO) and polystyrene sphere@polydopamine (PS@PDA) is the key factor to form the self-closure aerogels and the graphene sheets wrapped onto the PS@PDAs are responsible for the formation of the baffle plates. When employed as the host material for Li–S batteries, the as-made SGA can contribute to promotion of the transport of electrons, increasing the sulfur loading, confining the dissolution and diffusion of lithium polysulfides, and accommodating the volume expansion. As a result, the as-made SGA–sulfur composite can deliver an outstanding cycling stability of 509 mA h g−1 after 400 cycles at 1C. The present work will provide a simple and effective approach to tuning the assembly of graphene and further configuring the tailor-made host materials for high-performance Li–S batteries.

Rational design of metal oxide hollow nanostructures decorated carbon nanosheets for superior lithium storage

Unique nanostructures and intimate interfaces in nanocomposites play great roles in enhancing performance for energy storage and conversion application. Though many studies have focused on graphene/metal oxide composites with weak interactions by physical loading or chemical anchoring, engineering of metal oxide hollow nanostructures (h-MO) and construction of strongly coupled interfaces between graphene and metal oxides still remain in their infancy. In this work, metal oxide hollow nanostructures were bound onto graphene nanosheets by graphitic carbon layers (the final hybrid is denoted as h-MO@C@G), which were confirmed by HRTEM observations. Polyvinylpyrrolidone (PVP) and its derived carbon play great roles in uniform loading and engineering of h-MO as well as intimate integration of MO with graphene nanosheets. Benefiting from the synergistic effects of MO hollow nanostructures and strongly coupled interfaces for structural robustness and enhanced lithiation kinetics, the resulting h-Fe2O3@C@G anodes exhibit long cycling life over 500 times and a high rate capacity of 430 mA h g−1 at 15 A g−1. More importantly, the strategy developed here can be easily extended to synthesize other single metal oxide (Co3O4, NiOx) or mixed metal oxide (FeNiOx) hollow nanostructures strongly coupled with graphene nanosheets, and they all exhibit excellent electrochemical performance.

Facile one-step synthesis of highly graphitized hierarchical porous carbon nanosheets with large surface area and high capacity for lithium storage

Hierarchical porous carbon nanosheets (HPCSs) were prepared from acrylic resin using FeCl3·6H2O as catalyst and ZnCl2 as activator. The as-obtained materials possess a nanosheet structure and a combination of high graphitization degree and large surface area (2109 m2 g−1). When incorporated into the anode of a Lithium Ion Battery (LIBs), the HPCSs achieve a maximum specific capacity of 1642 mA h g−1 at 100 mA g−1 and 1100 mA h g−1 at 500 mA g−1 after 150 cycles, exhibiting enormous potential in developing advanced high performance LIBs. This work offers a facile strategy for the preparation of hierarchical porous carbon materials with high performance in LIBs from resin.