Mingyang Yang

Highly durable organic electrode for sodium-ion batteries via a stabilized α-C radical intermediate.

It is a challenge to prepare organic electrodes for sodium-ion batteries with long cycle life and high capacity. The highly reactive radical intermediates generated during the sodiation/desodiation process could be a critical issue because of undesired side reactions. Here we present durable electrodes with a stabilized α-C radical intermediate. Through the resonance effect as well as steric effects, the excessive reactivity of the unpaired electron is successfully suppressed, thus developing an electrode with stable cycling for over 2,000 cycles with 96.8% capacity retention. In addition, the α-radical demonstrates reversible transformation between three states: C=C; α-C·radical; and α-C− anion. Such transformation provides additional Na+ storage equal to more than 0.83 Na+ insertion per α-C radical for the electrodes. The strategy of intermediate radical stabilization could be enlightening in the design of organic electrodes with enhanced cycling life and energy storage capability.

Facile electrodeposition of 3D concentration-gradient Ni-Co hydroxide nanostructures on nickel foam as high performance electrodes for asymmetric supercapacitors

Novel three-dimensional (3D) concentration-gradient Ni-Co hydroxide nanostructures (3DCGNC) have been directly grown on nickel foam by a facile stepwise electrochemical deposition method and intensively investigated as binder- and conductor-free electrode for supercapacitors. Based on a three-electrode electrochemical characterization technique, the obtained 3DCGNC electrodes demonstrated a high specific capacitance of 1,760 F·g−1 and a remarkable rate capability whereby more than 62.5% capacitance was retained when the current density was raised from 1 to 100 A·g−1. More importantly, asymmetric supercapacitors were assembled by using the obtained 3DCGNC as the cathode and Ketjenblack as a conventional activated carbon anode. The fabricated asymmetric supercapacitors exhibited very promising electrochemical performances with an excellent combination of high energy density of 103.0 Wh·kg−1 at a power density of 3.0 kW·kg−1, and excellent rate capability—energy densities of about 70.4 and 26.0 Wh·kg−1 were achieved when the average power densities were increased to 26.2 and 133.4 kW·kg−1, respectively. Moreover, an extremely stable cycling life with only 2.7% capacitance loss after 20,000 cycles at a current density of 5 A·g−1 was achieved, which compares very well with the traditional doublelayer supercapacitors.

Large-scale fabrication of porous carbon-decorated iron oxide microcuboids from Fe–MOF as high-performance anode materials for lithium-ion batteries

A facile, cost-effective and environmentally friendly route has been developed to synthesise porous carbon-decorated iron oxides on a large scale via annealing iron metal–organic framework (MOF) precursors. The as-prepared C–Fe3O4 particles exhibit microcuboid-like morphologies that are actually composed of ultrafine nanoparticles and show a greatly enhanced lithium storage performance with high specific capacity, excellent cycling stability and good rate capability. The C–Fe3O4 electrodes demonstrate a high reversible capacity of 975 mA h g−1 after 50 cycles at a current density of 100 mA g−1 and a remarkable rate performance, with capacities of 1124, 1042, 886 and 695 mA h g−1 at current densities of 100, 200, 500 and 1000 mA g−1, respectively. The satisfactory electrochemical performance was attributed to the hierarchical architecture, which benefitted from the synergistic effects of the high conductivity of the carbon matrix, the cuboid-like secondary particles on the microscale, and the ultrafine primary nanoparticles on the nanoscale. This low-cost and simple method provides the possibility to prepare anode materials on a large scale and hence may have great potential applications in energy storage and conversion.

Facile Synthesis of Vanadium-Doped Ni3S2 Nanowire Arrays as Active Electrocatalyst for Hydrogen Evolution Reaction

Ni3S2 nanowire arrays doped with vanadium(V) are directly grown on nickel foam by a facile one-step hydrothermal method. It is found that the doping can promote the formation of Ni3S2 nanowires at a low temperature. The doped nanowires show excellent electrocatalytic performance toward hydrogen evolution reaction (HER), and outperform pure Ni3S2 and other Ni3S2-based compounds. The stability test shows that the performance of V-doped Ni3S2 nanowires is improved and stabilized after thousands of linear sweep voltammetry test. The onset potential of V-doped Ni3S2 nanowire can be as low as 39 mV, which is comparable to platinum. The nanowire has an overpotential of 68 mV at 10 mA cm-2, a relatively low Tafel slope of 112 mV dec-1, good stability and high Faradaic efficiency. First-principles calculations show that the V-doping in Ni3S2 extremely enhances the free carrier density near the Fermi level, resulting in much improved catalytic activities. We expect that the doping can be an effective way to enhance the catalytic performance of metal disulfides in hydrogen evolution reaction and V-doped Ni3S2 nanowire is one of the most promising electrocatalysts for hydrogen production.

Binder-free hydrogenated NiO–CoO hybrid electrodes for high performance supercapacitors

Binder-free NiO–CoO hybrid electrodes were directly grown on nickel foam by electrodeposition and subsequent annealing in 5% H2/95% N2 gas at 300 °C. Crystal structure, elemental analysis, surface morphology and chemical compositions of the composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with an energy dispersive X-ray analysis system. The hydrogenated NiO–CoO hybrid electrodes were evaluated as electrodes for supercapacitors which demonstrated promising electrochemical performance with high specific capacitance, excellent rate capability, and stable cycling.

Low-Cost and Novel Si-Based Gel for Li-Ion Batteries

Si-based nanostructure composites have been intensively investigated as anode materials for next-generation lithium-ion batteries because of their ultra-high-energy storage capacity. However, it is still a great challenge to fabricate a perfect structure satisfying all the requirements of good electrical conductivity, robust matrix for buffering large volume expansion, and intact linkage of Si particles upon long-term cycling. Here, we report a novel design of Si-based multicomponent three-dimensional (3D) networks in which the Si core is capped with phytic acid shell layers through a facile high-energy ball-milling method. By mixing the functional Si with graphene oxide and functionalized carbon nanotube, we successfully obtained a homogeneous and conductive rigid silicon-based gel through complexation. Interestingly, this Si-based gel with a fancy 3D cross-linking structure could be writable and printable. In particular, this Si-based gel composite delivers a moderate specific capacity of 2711 mA h g-1 at a current density of 420 mA g-1 and retained a competitive discharge capacity of more than 800.00 mA h g-1 at the current density of 420 mA g-1 after 700 cycles. We provide a new method to fabricate durable Si-based anode material for next-generation high-performance lithium-ion batteries.

Graphitized porous carbon prepared from pyrolysis of Sterculia scaphigera and its application in lithium ion batteries

Sterculia scaphigera exhibits exceptional capability to inhale a large amount of water, which is accompanied by great volume expansion. In this study, we present, for the first time, the eco-friendly preparation of graphitic porous carbon materials via a simple pyrolysis of H2O-adsorbed Sterculia scaphigera under moderate temperature. Nitrogen adsorption/desorption, X-ray diffraction, Raman spectra and transmission electron microscopy characterizations indicate that water adsorption plays a critical role in developing the abundant micropore architectures and high specific surface area as well as promoting the graphitization degree of the as-obtained porous carbon. Furthermore, the as-prepared porous carbon demonstrated superior electrochemical performance with a good combination of moderated capacity, good rate capability, extremely stable cycling and high coulombic efficiency.