Huiyu Yang

Controlled synthesis of V2O5/MWCNT core/shell hybrid aerogels through a mixed growth and self-assembly methodology for supercapacitors with high capacitance and ultralong cycle life

Vanadium pentoxide (V2O5)/multiwalled carbon nanotube (MWCNT) core/shell hybrid aerogels with different MWCNT contents are controlled synthesized through a facile mixed growth and self-assembly methodology. V2O5 coated MWCNTs from the in situ growth of V2O5 on the surface of acid-treated MWCNTs incorporate with V2O5 nanofibers from the preferred orientation growth of V2O5 in a one-step sol–gel process. These two kinds of one-dimensional fibers self-assemble into a three-dimensional monolithic porous hybrid aerogel. Owing to its high specific surface area, favorable electrical conductivity and unique three-dimensional and core/shell structures, the light weight hybrid aerogel (about 30 mg cm−3) exhibits excellent specific capacitance (625 F g−1), high energy density (86.8 W h kg−1) and outstanding cycle performance (>20000 cycles). And the optimal content of MWCNTs in hybrid aerogels for the highest-performance supercapacitor is 7.6%.

Multiwalled carbon nanotubes–V2O5 integrated composite with nanosized architecture as a cathode material for high performance lithium ion batteries

Multiwalled carbon nanotubes (MWCNTs)–V2O5 integrated composite with nanosized architecture has been synthesized through hydrothermal treatment combined with a post-sintering process. During the hydrothermal reaction, protonated hexadecylamine (C16H33NH3+) acts as an intermediator, which links the negatively charged vanadium oxide layer with the mixed-acid pretreated MWCNTs by weak electrostatic forces to form a three-phase hybrid (MWCNTs–C16–VOx). MWCNT–V2O5 composite and V2O5 nanoparticles can be obtained by sintering MWCNTs–C16–VOx at 400 and 550 °C in air, respectively. Among them, MWCNTs–V2O5 possesses better electrochemical performance as a cathode material for lithium ion batteries (LIBs). The unique porous nanoarchitecture of MWCNTs–V2O5 provides a large specific surface area and a good conductive network, which facilitates fast lithium ion diffusion and electron transfer. Additionally, the uniformly dispersed MWCNTs conducting network also behaves as an effective buffer which can relax the strain generated during charge–discharge cycles. Electrochemical tests reveal that MWCNTs–V2O5 could deliver a superior specific capacity (402 mA h g−1 during initial discharge at a current density of 100 mA g−1 between 1.5 and 4 V versus Li/Li+), good cycling stability (222 mA h g−1 after 50 cycles) and high rate capability (194 mA h g−1 at a current density of 800 mA g−1).

MgVPO4F as a one-dimensional Mg-ion conductor for Mg ion battery positive electrode: a first principles calculation

MgVPO4F is proposed as a cathode material for rechargeable Mg ion batteries for the first time. First principles calculations were performed to study the electrochemical properties of MgVPO4F as a positive electrode material for rechargeable Mg ion batteries. Our theoretical study gives an expectation of good battery performance by MgVPO4F.

A new method to prepare vanadium oxide nano-urchins as a cathode for lithium ion batteries

Urchin-like vanadium oxide nanotube clusters, abbreviated to VOx-NUs, were synthesized using a new method. Vanadium pentoxide, having a layered structure, was modified by lithium fluoride (LiF) and transformed into bi-phase lithium vanadate as the inorganic precursor. Then, VOx-NUs were prepared by hydrothermal reaction with dodecylamine as a template. This is different from other molecular assembly methods reported. VOx-NUs-350 nano clusters were obtained by annealing VOx-NUs at a temperature of 350 °C in air. Both samples were identified as three dimensional urchin-like nano clusters. Based on the characterization data obtained, a formation mechanism was established. By simply varying the LiF stoichiometric ratio, the nano tube density of the VOx-NUs could be controlled. VOx-NUs presented a higher initial rate capacity of 400 mA h g−1 and VOx-NUs-350 maintained a better capacity of 150 mA h g−1 after 50 cycles at a 100 mA g−1 current density between 1.5 and 4 V versus Li/Li+.

A facile method to prepare bi-phase lithium vanadate as cathode materials for Li-ion batteries

Bi-crystal lithium vanadate is synthesized with starting materials of V2O5 and LiF by one-step solid-state reaction. Since fluorine reacts with crucible made of silica, Li0.3V2O5-liked and LiV3O8-liked phases without F coexist in the produces. The stoichiometric proportion of two phases depends on the amount of dopant LiF. These are confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and transmission electron microscopy (TEM). Charge and discharge curves of bi-crystal materials present better reversibility of voltage plateaus than that of pure V2O5. The initial discharge capacity of Li0.3V2O5-liked phase dominated bi-crystal material is higher than pure V2O5. LiV3O8-liked phase dominated bi-crystal material has lower initial discharge capacity but delivers better cycling performance. Electrochemical impedance spectroscopy (EIS) measurements are performed to evaluate electrochemical kinetics of the bi-crystal materials. The results indicate that bi-crystal phase benefit the transfer resistance, interior diffusion resistance, and structure stability. Cathodes with different bi-phase structures have variable charge transfer resistance and lithium-ion diffusion speed due to this special structure.

Novel three-dimensional island-chain structured V2O5/graphene/MWCNT hybrid aerogels for supercapacitors with ultralong cycle life

Novel three-dimensional (3D) island-chain structured vanadium pentoxide (V2O5)/graphene (GN)/multiwalled carbon nanotube (MWCNT) hybrid aerogels (VGMA) are synthesized by a sol–gel method. In this process, V2O5 in situ grows along the surface of both MWCNT and GN by the coordination effect. These two kinds of one-dimensional fibers (V2O5 nanofibers and V2O5 coated MWCNT) and one kind of two-dimensional sheets (GN) co-assemble into a 3D porous island-chain structure. VGMA exhibit enhanced specific capacitance (504 F g−1), large energy density (70 W h kg−1) and outstanding cyclic property (82.9% retention after 32 500 cycles). All these excellent electrochemical properties of ternary VGMA can be attributed to the well-designed nanostructure and synergistic effect of the individual components. This also demonstrates that the unique island-chain nanostructured VGMA can be a good candidate for supercapacitors.

Study of lithium diffusion through vanadium pentoxide aerogel

Good electrode materials play an important part in rechargeable Li batteries. In this paper, safe and inexpensive vanadium pentoxide (V2O5) aerogel materials were used as cathode materials. We discussed preparation of the films and lithium ion diffusion at the interface between the cathode and electrolyte by potential-step current transient technique and digital simulations. The results showed that diffusion coefficient (DLi) of the V2O5 aerogel film was 9.18×10-14cm2/s and exchange current was 12.5×10-6A at potential step 3.6~3.5VLi/Li+.

Optical and electrochemical properties of vanadium pentoxide porous film prepared by sol-gel technique

Thin films of V2O5, especially vanadium oxide films with nano- and micro-structures, perform well as cathode material for Li ion batteries and charge storage devices. Thin films of V2O5 with different porosity were obtained by dip-coating sol-gel technique. V2O5 sols were prepared by dissolution of V2O5 powder in benzyl alcohol and isopropyl alcohol in proper proportion. Optical property and porosity of films were characterized by FTIR and ellipsometer. Electrochemical characterization was recorded by chronopotentiometry(CP) and cyclic voltammetry(CV). Furthermore, the study shows that the porous structures of V2O5 films had an effect on the stability and reversibility of the films.