Q.Q. Xiong

Hierarchical NiCo2O4@NiCo2O4 Core/Shell Nanoflake Arrays as High-Performance Supercapacitor Materials

Hierarchical NiCo2O4@NiCo2O4 core/shell nanoflake arrays on nickel foam for high-performance supercapacitors are fabricated by a two-step solution-based method which involves in hydrothermal process and chemical bath deposition. Compared with the bare NiCo2O4 nanoflake arrays, the core/shell electrode displays better pseudocapacitive behaviors in 2 M KOH, which exhibits high areal specific capacitances of 1.55 F cm(-2) at 2 mA cm(-2) and 1.16 F cm(-2) at 40 mA cm(-2) before activation as well as excellent cycling stability. The specific capacitance can achieve a maximum of 2.20 F cm(-2) at a current density of 5 mA cm(-2), which can still retain 2.17 F cm(-2) (98.6% retention) after 4000 cycles. The enhanced pseudocapacitive performances are mainly attributed to its unique core/shell structure, which provides fast ion and electron transfer, a large number of active sites, and good strain accommodation.

Co3O4–C core–shell nanowire array as an advanced anode material for lithium ion batteries

We report on the synthesis of a Co3O4–C core–shell nanowire array and its application as an anode material for lithium ion batteries. The core–shell nanowire array is prepared by combining a facial hydrothermal synthesis and direct current magnetron sputtering. The amorphous carbon layer with a thickness of 18 nm is homogeneously coated on the surface of the porous Co3O4 nanowire. The Co3O4–C core–shell nanowire array delivers an initial discharge capacity of 1330.8 mA h g−1 at 0.5 C and maintains a high reversible capacity of 989.0 mA h g−1 after 50 cycles, much higher than the unmodified Co3O4 nanowire array (490.5 mA h g−1). The improved electrochemical performance can be attributed to the introduction of a thin carbon layer, which improves the electrical conductivity and structure stability of the Co3O4 nanowire array.

A three-dimensional hierarchical Fe2O3@NiO core/shell nanorod array on carbon cloth: a new class of anode for high-performance lithium-ion batteries

A Fe2O3@NiO core/shell nanorod array on carbon cloth was prepared with the aid of hydrothermal synthesis combined with subsequent chemical bath deposition. The resultant array structure is composed of Fe2O3 nanorods as the core and interconnected ultrathin NiO nanoflakes as the shell. As an anode material for lithium-ion batteries, the heterostructured array electrode delivers a high discharge capacity of 1047.2 mA h g(-1) after 50 cycles at 200 mA g(-1), and 783.3 mA h g(-1) at a high current density of 2000 mA g(-1). The excellent electrochemical performance is attributed to the unique 3D core/shell nanorod array architecture and a rational combination of two electrochemical active materials. Our growth approach offers a simple and effective technique for the design and synthesis of a transition metal oxide hierarchical array that is promising for high-performance electrochemical energy storage.

Self-assembly of hierarchical Fe3O4 microsphere/graphene nanosheet composite: towards a promising high-performance anode for Li-ion batteries

A hierarchical Fe3O4 microsphere/graphene nanosheet (H-Fe3O4-MS/GNS) composite has been synthesized by a facile one-pot solvothermal route. The Fe3O4 microspheres uniformly decorated the surface of the two dimensional GNS. Each Fe3O4 microsphere possesses a hierarchical and porous structure, which is composed of Fe3O4 nanoparticles with a diameter of about 10 nm. As an anode material for Li-ion batteries, the H-Fe3O4-MS/GNS composite shows high specific capacity and good cycling stability (1171.6 mA h g−1 at 200 mA g−1 and 940.4 mA h g−1 at 500 mA g−1 up to 70 cycles), reduced voltage hysteresis, as well as enhanced rate capability. The improved electrochemical performance can be attributed to the combination of the conductivity, confinement and dispersion effects of GNS and the porous hierarchical structure of the Fe3O4 microsphere.

Three-dimensional porous nano-Ni/Fe3O4 composite film: enhanced electrochemical performance for lithium-ion batteries

A novel 3D porous nano-Ni/Fe3O4 composite film is prepared by electrodepositing 3D porous nano-Ni onto a Cu current collector followed by electrochemical plating of Fe3O4 nanoflakes. As an anode material for lithium-ion batteries, the resultant 3D porous nano-Ni/Fe3O4 composite film shows an improved initial columbic efficiency of 86.0%, high capacity and good cycle stability (951.9 mA h g−1 at 1 C up to 50 cycles), as well as enhanced rate capability. This unique electrode configuration possesses the following features: high Fe3O4− electrolyte contact area, direct contact between each naonflake and its ‘own’ current collector of nano-Ni, fast Li+ diffusion and better accommodation of volume change. It suggests that the 3D porous nano-Ni/Fe3O4 composite film, synthesized by the two-step electrodeposition strategy, is a promising anode material for high energy-density lithium-ion batteries.

Hierarchical structure Ti-doped WO3 film with improved electrochromism in visible-infrared region

Hierarchical structure Ti-doped WO3 thin films are prepared by a template-free hydrothermal method. The influence of Ti doping on the electrochromic properties of WO3 thin films is investigated in the visible-infrared region. Ti doping can lead to significant surface morphology change and lower the crystallization, which plays an important role in the electrochromic properties of WO3 films. The large transmittance modulation (49.1% at 750 nm, 64.6% at 2000 nm and 59.3% at 10 μm), fast switching speed (1.7 s and 1.6 s) and high coloration efficiency (68 cm2 C−1 at 750 nm) are achieved for the low Ti-doped WO3 film. The enhancement in the electrochromic performance of the low Ti-doped WO3 films is attributed to their low crystallization, a star-like structure which has low charge transfer and ion diffusion resistance, leading to superior electrical conductivity and reaction kinetics.

Carbon‐Decorated Single‐Crystalline Ni2P Nanotubes Derived from Ni Nanowire Templates: A High‐Performance Material for Li‐Ion Batteries

Single-crystalline Ni(2)P nanotubes (NTs) were facilely synthesized by using a Ni nanowire template. The mechanism for the formation of the tubular structures was related to the nanoscale Kirkendall effect. These NTs exhibited a core/shell structure with an amorphous carbon layer that was grown in situ by employing oleylamine as a capping agent. Galvanostatic charge/discharge measurements indicated that these Ni(2)P/C NTs exhibited superior high-rate capability and good cycling stability. There was still about 310 mA h  g(-1) retained after 100 cycles at a rate of 5 C. Importantly, the tubular nanostructures and the single-crystalline nature of the Ni(2)P NTs were also preserved after prolonged cycling at a relatively high rate. These improvements were attributed to the stable nanotubular structure of Ni(2)P and the carbon shell, which enhanced the conductivity of Ni(2)P, suppressed the aggregation of active particles, and increased the electrode stability during cycling.

Synthesis of dinickel phosphide (Ni2P) for fast lithium-ion transportation: a new class of nanowires with exceptionally improved electrochemical performance as a negative electrode

Single-crystalline dinickel phosphide (Ni2P) nanowires with a uniform diameter of about 8 nm and lengths of 100–200 nm were synthesized from the thermal decomposition of continuously delivered Ni-TOP complexes using a syringe pump. These Ni2P nanowires deliver specific reversible capacities of 434 mA h g−1 at 0.1 C, 326 mA h g−1 at 0.5 C after 50 cycles, and also exhibit good rate performance. The improved electrochemical performance is attributed to the small size and stable cylindrical structure, which result in a high interfacial contact area with the electrolyte, and relieve the strain or accommodate volume expansion/contraction of these Ni2P nanowires. Electrochemical impedance spectra confirms that these Ni2P nanowires possess enhanced electrical conductivity, which facilitates the lithium ion and electron transportation in the electrode.

Large-scale synthesis of porous Ni2P nanosheets for lithium secondary batteries

Porous Ni2P nanosheets were synthesized via a facile organometallic method based on Ni nanosheet template. These Ni2P nanosheets exhibit an extremely thin thickness of about 3 nm and a high Brunauer–Emmett–Teller (BET) surface area due to their highly porous structure. As promising anode materials for lithium ion batteries, these nanosheets present a reversible discharge capacity of 379.8 mAh g−1 after 50 cycles, as well as a good rate capability. The improved electrochemical performances of Ni2P nanosheet electrodes are attributed to the porous and thin sheet structure, resulting in better contact between the active material and electrolyte. Importantly, the thin porous Ni2P sheets would lead to a short diffusion length of lithium ions.