Xusong Liu

Assembly of flexible CoMoO 4 @NiMoO 4 ·xH 2 O and Fe 2 O 3 electrodes for solid-state asymmetric supercapacitors

In this work, CoMoO4@NiMoO4·xH2O core-shell heterostructure electrode is directly grown on carbon fabric (CF) via a feasible hydrothermal procedure with CoMoO4 nanowires (NWs) as the core and NiMoO4 nanosheets (NSs) as the shell. This core-shell heterostructure could provide fast ion and electron transfer, a large number of active sites, and good strain accommodation. As a result, the CoMoO4@NiMoO4·xH2O electrode yields high-capacitance performance with a high specific capacitance of 1582 F g−1, good cycling stability with the capacitance retention of 97.1% after 3000 cycles and good rate capability. The electrode also shows excellent mechanical flexibility. Also, a flexible Fe2O3 nanorods/CF electrode with enhanced electrochemical performance was prepared. A solid-state asymmetric supercapacitor device is successfully fabricated by using flexible CoMoO4@NiMoO4·xH2O as the positive electrode and Fe2O3 as the negative electrode. The asymmetric supercapacitor with a maximum voltage of 1.6 V demonstrates high specific energy (41.8 Wh kg−1 at 700 W kg−1), high power density (12000 W kg−1 at 26.7 Wh kg−1), and excellent cycle ability with the capacitance retention of 89.3% after 5000 cycles (at the current density of 3A g−1).

Rational selection of amorphous or crystalline V2O5 cathode for sodium-ion batteries

Vanadium oxide (V2O5), as a potential positive electrode for sodium ion batteries (SIBs), has attracted considerable attention from researchers. Herein, amorphous and crystalline V2O5 cathodes on a graphite paper without a binder and conductive additives have been synthesized via facile anodic electrochemical deposition following different heat treatments. Both the amorphous V2O5 (a-V2O5) cathode and crystalline V2O5 (c-V2O5) cathode show good rate cycling performance and long cycling life. After five rate cycles, the reversible capacities of both the cathodes were almost unchanged at different current densities from 40 to 5120 mA g-1. Long cycling tests with 10 000 cycles were carried out and the two cathodes exhibit excellent cycling stability. The c-V2O5 cathode retains a high specific capacity of 54 mA h g-1 after 10 000 cycles at 2560 mA g-1 and can be charged within 80 s. Interestingly, the a-V2O5 cathode possesses higher reversible capacities than the c-V2O5 cathode at low current densities, whereas it is inversed at high current densities. The c-V2O5 cathode shows faster capacity recovery from 5120 to 40 mA g-1 than the a-V2O5 cathode. When discharged at 80 mA g-1 (long discharge time of 140 min) and charged at 640 mA g-1 (short charge time of 17 min), the a-V2O5 cathode shows a higher discharge capacity than its c-V2O5 counterpart. The different electrochemical performance of a-V2O5 and c-V2O5 cathodes during various electrochemical processes can provide a rational selection of amorphous or crystalline V2O5 cathode materials for SIBs in their practical applications to meet the variable requirements.

Controlling the hydrothermal growth and the properties of ZnO nanorod arrays by pre-treating the seed layer

Dense arrays of ultra-thin zinc oxide (ZnO) nanorods have been fabricated on c-oriented ZnO seed layers by hydrothermal growth, with particular emphasis on exploring the effects of annealing or plasma pre-treating the seed layer. Such pre-treatments influence the density, size and surface defects of particles within the nucleating seed layer, which impacts on the subsequent nanorod growth via sequential reaction with OH− and Zn2+ species. Oxygen-rich defects at the seed layer surface are deduced to have particular impact – affecting both the c-axis growth rate and the photoluminescence properties of the as-grown nanorods.

Improved cycling stability of MoS2-coated carbon nanotubes on graphene foam as flexible anodes for lithium-ion batteries

Achieving appropriate cycling stability for metal sulfides used as anodes in Li-ion batteries remains highly challenging because of structural collapse or low conductivity. Herein, a novel composite was designed as an anode material for Li-ion batteries. This unique architecture has the advantages of a large interface area, numerous channels for Li+ and electron transport, and a porous structure that facilitates electrolyte infiltration and buffers the volume expansion. As expected, this composite exhibits good cycling stability, high reversible capacity, and high rate capability, delivering a high discharge capacity of 1511.6 mA h g−1 and a high first columbic efficiency of 83.27%. The reversible capacities of graphitic-carbon network material (GCNM) electrodes are 1112 mA h g−1 at a current density of 0.1 A g−1 after 100 cycles, and they show superior rate capabilities. This GCNM composite demonstrates great potential for applications in power sources for flexible and lightweight electronic devices.

Ionic liquid electrodeposition of 3D germanium–acetylene black–Ni foam nanocomposite electrodes for lithium-ion batteries

A simple process involving the electrophoretic deposition of acetylene black onto Ni foam and the ionic liquid electrodeposition of Ge has been used to synthesize a 3D Ge–acetylene black–Ni foam electrode material at room temperature. Electrochemical measurements demonstrate that when applied in a lithium ion battery, this material exhibits a high capacity of up to 924 mA h g−1 after 100 cycles at 0.1 C and a high rate capability at 1 C and 5 C rates of 1210 and 524 mA h g−1, respectively. This high electrochemical performance is the result of the 3D acetylene black network enhancing electron migration, while also providing sufficient elasticity to buffer the volume expansion of the Ge nanoparticles.

Ionic liquid electrodeposition of Ge nanostructures on freestanding Ni-nanocone arrays for Li-ion battery

With the growing demand for portable and wearable electronic devices, it is imperative to develop high-performance Li-ion batteries with long lifetimes. The deployment of three-dimensional (3D) nanostructured materials on current collectors has recently emerged as a promising strategy for preparing high-performance Li-ion batteries. We develop a simple and efficient method for fabricating ultrathin and flexible 3D Ge–Ni nanocone arrays (NCAs) electrode materials using a two-step electrodeposition process. With uniform NCAs as the substrate, Ge nanoparticles were deposited from ionic liquid at room temperature. The electrode can be removed from the carrier film. Thus, the resulting freestanding electrode can be as thin as 3 μm and exhibits specific capacity up to 500 mA h g−1 after 100 cycles at 0.1 C, the rate capability at 1 C and 2 C rates of 700 mA h g−1 and 400 mA h g−1, respectively. This improved electrochemical performance is the result of the 3D NCAs enhanced electron migration and electron transport paths while also providing sufficient elasticity to buffer the volume expansion of the Ge nanoparticles.

Three dimensional hierarchically porous crystalline MnO2 structure design for a high rate performance lithium-ion battery anode

A reasonably designed anode of hierarchically porous crystalline manganese dioxide on nickel foam has been successfully synthesized by facile anodic electrochemical deposition in combination with heat treatment. The three dimensional structure avoids the application of binder and conductive additives. The Ni foam provides a highly electronically conductive network in conjunction with a large surface area to support well contacted MnO2 nanoparticles and effectively increases the mechanical strength of the MnO2 anode as well as suppresses the aggregation of MnO2 nanoparticles during discharge/charge processes. The hierarchical pores composed of a large amount of macropores and mesopores can not only accommodate the volume change of MnO2 nanoparticles during Li ion insertion/extraction, but also accelerate the penetration of electrolyte and promise fast transport and intercalation kinetics of Li ions. The crystalline MnO2 anode exhibits a higher electrochemical performance than the amorphous one. As a result, the hierarchically porous crystalline MnO2 anode shows a long cycling life of 778.0 mA h g−1 after 200 cycles at a current density of 0.4 A g−1 and high-rate capability of up to 82% capacity retention even after the current density increases 20 times from 0.1 to 2.0 A g−1.

Reagent concentration dependent variations in the stability and photoluminescence of silica-coated ZnO nanorods

Silica (SiO2) coating is finding increasing use as a means of improving the properties of ZnO nanomaterials. However, the current literature contains seemingly contradictory reports of the effect of such coatings on their photoluminescence (PL) properties. Two types of ZnO nanorod (henceforth termed Types A and B) were synthesized using the same hydrothermal method (differing only in the chosen precursor concentrations), then subjected to the exact same SiO2-coating procedure. SiO2 coating is seen to have a strikingly different effect on the Type A and B nanorod morphologies and their PL. In the case of Type A nanorods, (i.e. nanorods grown using high precursor concentrations), SiO2 coating has no discernible morphological effect but causes an obvious increase in the intensity of the visible component within the PL emission. Type B nanorods (grown from 20-times less concentrated reactive solution), in contrast, show a very different response to SiO2 coating: morphologically, they appear as many ZnO nanodots in the silica shell that surrounds the etched ZnO core, and their ultraviolet PL is boosted. Systematic investigation of the effects of various other post-treatments on the PL from Type A and B nanorods leads to the conclusion that the different responses to SiO2 coating can be traced to the different nanorod growth chemistries – i.e. by precipitation from Zn(OH)2 intermediates (Type A nanorods) or by direct reaction of Zn2+ and OH− ions (Type B material). The present study advances our understanding both of the controlled synthesis and of routes to optimising the properties of bare and silica-coated ZnO nanomaterials for nanodevice applications.

The binder-free Ca2Ge7O16 nanosheet/carbon nanotube composite as a high-capacity anode for Li-ion batteries with long cycling life

We report a facile one-step route to synthesize a Ca2Ge7O16 nanosheet (NS)/carbon nanotube (CNT) anode for the first time. The Ca2Ge7O16 NS/CNT composites are uniformly grown on the surface of three-dimensional Ni foam used as the conductive current collector. The Ca2Ge7O16 NS/CNT composite is used as a binder-free anode for lithium-ion batteries, which delivers a reversible capacity of 998.5 mA h g−1 at a current rate of 0.5 A g−1 and exhibits excellent cycle performance (87% retention of its 2nd cycle reversible capacity after 1000 cycles). Furthermore, a binder free full cell is fabricated, which shows excellent cycle performance with 96% retention of its 10th cycle capacity after 100 cycles. The superior cycling performance is attributed to the synergetic effect of small diffusion lengths in NS, sufficient void space to buffer the volume expansion, the CNT for charge transport and a continuous 3D electronic path of the Ni foam.

Template-free growth of coral-like Ge nanorod bundles via UV-assisted ionic liquid electrodeposition

Germanium (Ge) is an important semiconductor material in optoelectronic devices and is being researched in energy storage fields. Ge nanostructure materials with different morphologies may lead to distinctly different application performances. In this work, Ge nanorod architectures were successfully template-free electrodeposited on ITO substrate from the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([Emim]Tf2N) containing dissolved GeCl4 with the assistance of UV light. The UV irradiation influences the conformation of imidazolium rings of [Emim]+ adsorbed during the deposition process. A solution template has been formed on the surface of the electrode which inhibited the lateral growth of Ge nuclei and promoted the growth of Ge nanorod structures. Consequently, the coral-like Ge nanorod bundles (NRBs) has been obtained. This method provides attractive prospects for the other semiconductor nanorod structures.