Huiqiao Li

Centimeter‐Long V2O5 Nanowires: From Synthesis to Field‐Emission, Electrochemical, Electrical Transport, and Photoconductive Properties

Adv. Mater. 2010, 22, 2547–2552 2010 WILEY-VCH Verlag G One-dimensional nanostructures have attracted considerable attention due to their importance in basic scientific research and potential technologic applications. Among them, vanadium pentoxide (V2O5) nanowires have been extensively studied in recent years because of their prospective applications in chemical sensors, field-emitters, catalysts, lithium-ion batteries, actuators, and electrochromic or other nanodevices. Several different approaches have been explored for the synthesis of V2O5 nanowires, such as thermal evaporation methods, hydrothermal/solvothermal syntheses, sol–gel techniques, and electrodeposition. However, the nanowires synthesized by these methods have typical lengths in the micrometer range (most of them are shorter than 10mm);moreover, if one canmake centimeter-long V2O5 nanowires, which should be much more useful compared to short wires for some specific purposes, such as field-emission (FE), device interconnects, and reinforcing fibers in composites. Herein, we fabricated high-quality single-crystalline centimeter-long V2O5 nanowires ( 80–120 nm in diameter, several centimeters in length; aspect ratio >10–10) using an environmental friendly hydrothermal approach without dangerous reagents, harmful solvents, and surfactants. The FE, electrochemical and electrical transport, and photoconductive properties of the synthesized V2O5 nanowires were then investigated in detail. Our results suggest a high potential of utilizing these novel nanowires in field-emitters, lithium-ion batteries, interconnects, and optoelectronic devices. The representative morphologies of the V2O5 nanowires were investigated by FE scanning electron microscopy (SEM), as shown in Figure 1a. Other SEM images (see the Supporting Information, Fig. S1) also confirm the high-yield fabrication of smooth and straight nanowires of 80–120 nm in diameter. Large portions of the nanowires are usually several millimeters or even up to several centimeters in length (inset of Fig. 1a), resulting in an aspect ratio of 10–10. To the best of our knowledge, this is the first time that such ultra-long V2O5 nanowires have been obtained. An X-ray diffraction (XRD) pattern of the sample is shown in Figure 1b. All the diffraction peaks can be indexed to an orthorhombic V2O5 phase with the lattice parameters of a1⁄4 11.54 A, b1⁄4 3.571 A, and c1⁄4 4.383 A, in good agreement with the literature values (Joint Committee on Powder Diffraction Standards (JCPDS) Card, no. 89-0612). No characteristic peaks of any impurities are detected in this pattern. Figure S2 (Supplementary Information) depicts a room temperature micro-Raman spectrum of the ultralong V2O5 nanowires. The peaks, located at 145, 197, 285, 305, 407, 480, 525, 694, and 990 cm , can be assigned to the Raman signature of V2O5. [18,19] A predominant low-wavelength peak at 145 cm 1 is attributed to the skeleton bent vibration (B3g mode), while the peaks at 197 and 285 cm 1 derive from the bending vibrations of OC V OB bond (Ag and B2g modes). The bending vibration of V OC (Ag mode), the bending vibration of V OB V bond (Ag mode), the stretching vibration of V OB V bond (Ag mode), and the stretching vibration of V OC bond (B2g mode) are regarded at about 305, 407, 525, and 694 cm , respectively. The layered structure of V2O5 is stacked up from distorted trigonal bipyramidal atoms that share edges to form (V2O4)n zigzag double chains along the [001] direction and are cross-linked along the [100] direction through the shared corners. The mode of a skeleton bent, corresponding to the peak at 145 cm , provides an evidence for the layered structure of V2O5. Furthermore, the narrow peak centered at 990 cm , corresponding to the stretching of vanadium atoms connected to oxygen atoms through double bonds (V1⁄4O), is also an additional clue to the layer-type structure of V2O5. [22,23] The detailed microstructures of V2O5 nanowires were further studied by transmission electron microscopy (TEM). Figure 2a shows a TEM image of V2O5 nanowires, which demonstrates that the V2O5 nanowires have uniform diameters throughout their entire lengths. An X-ray energy-dispersive spectrum (EDS) acquired from an individual nanowire exhibits strong V and O peaks. The atomic ratio of V and O is close to the 2:5

Ultrathin SnSe2 Flakes Grown by Chemical Vapor Deposition for High‐Performance Photodetectors

High-quality ultrathin single-crystalline SnSe2 flakes are synthesized under atmospheric-pressure chemical vapor deposition for the first time. A high-performance photodetector based on the individual SnSe2 flake demonstrates a high photoresponsivity of 1.1 × 10(3) A W(-1), a high EQE of 2.61 × 10(5)%, and superb detectivity of 1.01 × 10(10) Jones, combined with fast rise and decay times of 14.5 and 8.1 ms, respectively.

One‐Dimensional CdS Nanostructures: A Promising Candidate for Optoelectronics

As a promising candidate for optoelectronics, one-dimensional CdS nanostructures have drawn great scientific and technical interest due to their interesting fundamental properties and possibilities of utilization in novel promising optoelectronical devices with augmented performance and functionalities. This progress report highlights a selection of important topics pertinent to optoelectronical applications of one-dimensional CdS nanostructures over the last five years. This article begins with the description of rational design and controlled synthesis of CdS nanostructure arrays, alloyed nanostructucures and kinked nanowire superstructures, and then focuses on the optoelectronical properties, and applications including cathodoluminescence, lasers, light-emitting diodes, waveguides, field emitters, logic circuits, memory devices, photodetectors, gas sensors, photovoltaics and photoelectrochemistry. Finally, the general challenges and the potential future directions of this exciting area of research are highlighted.

Self-stacked Co3O4 nanosheets for high-performance lithium ion batteries.

Self-stacked Co(3)O(4) nanosheets separated by carbon layers were synthesized via a facile method. They exhibit excellent electrochemical performance that results from superior electronic conductivity endowed by carbon, a reduced Li(+) diffusion length within the building blocks and a large electrode/electrolyte contact area due to the interspaces between the blocks.

High-surface vanadium oxides with large capacities for lithium-ion batteries: from hydrated aerogel to nanocrystalline VO2(B), V6O13 and V2O5

Vanadium pentoxide aerogels with high surface area (196 m2 g−1) and ultrathin nanofiber (∼10 nm) morphology were prepared through a sol–gel method followed by a freeze-drying process. Such amorphous aerogels were used as a versatile precursor to synthesize vanadium oxides with diverse valences and crystallographic phases. By simply controlling the calcination atmosphere and temperature, we can successfully obtain nanocrystalline VO2(B), V6O13 and V2O5 at high vacuum, pure Ar and air atmosphere, respectively. The evolutions in morphology, structure, crystallization, chemical composition and consequent electrochemical performances upon different calcinations were discussed in detail. These derivative vanadium oxides well inherited the unique structural features of their aerogel precursors, e.g., high surface area, mesoporous network, and nanofibrous morphology, and thus delivered enhanced electrochemical performances comparing with their bulk counterparts when used as the electrode materials for lithium-ion batteries. The larger capacities of these vanadium oxides derived from aerogels were attributed to their high surface area and nanofiber structure which promise both high reaction active surface and short Li+ diffusion paths upon Li+ intercalation/de-intercalation.

Reviving Lithium-Metal Anodes for Next-Generation High-Energy Batteries

Lithium-metal batteries (LMBs), as one of the most promising next-generation high-energy-density storage devices, are able to meet the rigid demands of new industries. However, the direct utilization of metallic lithium can induce harsh safety issues, inferior rate and cycle performance, or anode pulverization inside the cells. These drawbacks severely hinder the commercialization of LMBs. Here, an up-to-date review of the behavior of lithium ions upon deposition/dissolution, and the failure mechanisms of lithium-metal anodes is presented. It has been shown that the primary causes consist of the growth of lithium dendrites due to large polarization and a strong electric field at the vicinity of the anode, the hyperactivity of metallic lithium, and hostless infinite volume changes upon cycling. The recent advances in liquid organic electrolyte (LOE) systems through modulating the local current density, anion depletion, lithium flux, the anode-electrolyte interface, or the mechanical strength of the interlayers are highlighted. Concrete strategies including tailoring the anode structures, optimizing the electrolytes, building artificial anode-electrolyte interfaces, and functionalizing the protective interlayers are summarized in detail. Furthermore, the challenges remaining in LOE systems are outlined, and the future perspectives of introducing solid-state electrolytes to radically address safety issues are presented.

Two-dimensional layered nanomaterials for gas-sensing applications

Owing to the unique thickness dependent physical and chemical properties, two-dimensional (2D) layered nanomaterials have received tremendous attention and shown great potential in the fabrication of high-performance electronic/optoelectronic devices. Notably, the implication of 2D nanomaterials in the gas-sensing field has also drawn considerable attention but few related review studies have been reported. This critical review mainly focuses on the current progress of 2D layered nanomaterials in gas-sensing applications. Firstly, we describe the basic attributes of 2D layered nanostructures and discuss the fundamentals of their gas-sensing applications. Secondly, we have numerated recent gas-sensing studies on typical 2D layered nanomaterials, including graphene, MoS2, MoSe2, WS2, SnS2, black phosphorus, and others. Particularly, the optimized strategies for improving their gas-sensing performances are also discussed here. Finally, we conclude this review with some perspectives and the outlook on future advances in this field.

Rechargeable Ni-Li battery integrated aqueous/nonaqueous system.

A rechargeable Ni-Li battery, in which nickel hydroxide serving as a cathode in an aqueous electrolyte and Li metal serving as an anode in an organic electrolyte were integrated by a superionic conductor glass ceramic film (LISICON), was proposed with the expectation to combine the advantages of both a Li-ion battery and Ni-MH battery. It has the potential for an ultrahigh theoretical energy density of 935 Wh/kg, twice that of a Li-ion battery (414 Wh/kg), based on the active material in electrodes. A prototype Ni-Li battery fabricated in the present work demonstrated a cell voltage of 3.47 V and a capacity of 264 mAh/g with good retention during 50 cycles of charge/discharge. This battery system with a hybrid electrolyte provides a new avenue for the best combination of electrode/electrolyte/electrode to fulfill the potential of high energy density as well as high power density.

The development of a new type of rechargeable batteries based on hybrid electrolytes.

Lithium ion batteries (LIBs), which have the highest energy density among all currently available rechargeable batteries, have recently been considered for use in hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and pure electric vehicles (PEV). A major challenge in this effort is to increase the energy density of LIBs to satisfy the industrial needs of HEVs, PHEVs, and PEVs. Recently, new types of lithium-air and lithium-copper batteries that employ hybrid electrolytes have attracted significant attention; these batteries are expected to succeed lithium ion batteries as next-generation power sources. Herein, we review the concept of hybrid electrolytes, as well as their advantages and disadvantages. In addition, we examine new battery types that use hybrid electrolytes.

Single-crystal H2V3O8 nanowires: a competitive anode with large capacity for aqueous lithium-ion batteries

Single-crystal H2V3O8 nanowires with a width of ∼50 nm were fabricated by a facile one-step hydrothermal method and SEM, TEM, TGA, XRD, XPS were used to characterize their morphology and structure details. The possibility of using this material as an anode candidate for aqueous lithium-ion batteries was investigated for the first time. CV and galvanostatic charge/discharge measurements indicated that the intercalation/deintercalation of Li+ in this material in aqueous electrolyte is highly reversible. A discharge capacity of 234 mAh g−1 can be obtained for the synthesized H2V3O8 nanowires at the current density of 0.1 A g−1 in aqueous solution of 5 M LiNO3 and 0.001 M LiOH, much larger than the available capacities (less than 110 mAh g−1) of other vanadium oxides in aqueous electrolyte. Furthermore, the H2V3O8 nanowires can be charge/discharged upon 50 cycles with nearly no capacity loss in organic electrolyte and a capacity retention over 70% in aqueous electrolyte, showing better cycle stability than other vanadium oxide predecessors for aqueous lithium-ion batteries.