Yanzhu Luo

Electrospun Ultralong Hierarchical Vanadium Oxide Nanowires with High Performance for Lithium Ion Batteries

Ultralong hierarchical vanadium oxide nanowires with diameter of 100-200 nm and length up to several millimeters were synthesized using the low-cost starting materials by electrospinning combined with annealing. The hierarchical nanowires were constructed from attached vanadium oxide nanorods of diameter around 50 nm and length of 100 nm. The initial and 50th discharge capacities of the ultralong hierarchical vanadium oxide nanowire cathodes are up to 390 and 201 mAh/g when the lithium ion battery cycled between 1.75 and 4.0 V. When the battery was cycled between 2.0 and 4.0 V, the initial and 50th discharge capacities of the nanowire cathodes are 275 and 187 mAh/g. Compared with self-aggregated short nanorods synthesized by hydrothermal method, the ultralong hierarchical vanadium oxide nanowires exhibit much higher capacity. This is due to the fact that self-aggregation of the unique nanorod-in-nanowire structures have been greatly reduced because of the attachment of nanorods in the ultralong nanowires, which can keep the effective contact areas of active materials, conductive additives, and electrolyte large and fully realize the advantage of nanomaterial-based cathodes. This demonstrates that ultralong hierarchical vanadium oxide nanowire is one of the most favorable nanostructures as cathodes for improving cycling performance of lithium ion batteries.

Cucumber-Like V2O5/poly(3,4-ethylenedioxythiophene)&MnO2 Nanowires with Enhanced Electrochemical Cyclability

Inspired by the cucumber-like structure, by combining the in situ chemical oxidative polymerization with facile soaking process, we designed the heterostructured nanomaterial with PEDOT as the shell and MnO(2) nanoparticles as the protuberance and synthesized the novel cucumber-like MnO(2) nanoparticles enriched vanadium pentoxide/poly(3,4-ethylenedioxythiophene) (PEDOT) coaxial nanowires. This heterostructured nanomaterial exhibits enhanced electrochemical cycling performance with the decreases of capacity fading during 200 cycles from 0.557 to 0.173% over V(2)O(5) nanowires at the current density of 100 mA/g. This method is proven to be an effective technique for improving the electrochemical cycling performance and stability of nanowire electrodes especially at low rate for application in rechargeable lithium batteries.

Fast Ionic Diffusion-Enabled Nanoflake Electrode by Spontaneous Electrochemical Pre-Intercalation for High-Performance Supercapacitor

Layered intercalation compounds NaxMnO2 (x = 0.7 and 0.91) nanoflakes have been prepared directly through wet electrochemical process with Na+ ions intercalated into MnO2 interlayers spontaneously. The as-prepared NaxMnO2 nanoflake based supercapacitors exhibit faster ionic diffusion with enhanced redox peaks, tenfold-higher energy densities up to 110 Wh·kg−1 and higher capacitances over 1000 F·g−1 in aqueous sodium system compared with traditional MnO2 supercapacitors. Due to the free-standing electrode structure and suitable crystal structure, NaxMnO2 nanoflake electrodes also maintain outstanding electrochemical stability with capacitance retention up to 99.9% after 1000 cycles. Besides, pre-intercalation effect is further studied to explain this enhanced electrochemical performance. This study indicates that the suitable pre-intercalation is effective to improve the diffusion of electrolyte cations and other electrochemical performance for layered oxides, and suggests that the as-obtained nanoflakes are promising materials to achieve the hybridization of both high energy and power density for advanced supercapacitors.

Rational Synthesis of Silver Vanadium Oxides/Polyaniline Triaxial Nanowires with Enhanced Electrochemical Property

We designed and successfully synthesized the silver vanadium oxides/polyaniline (SVO/PANI) triaxial nanowires by combining in situ chemical oxidative polymerization and interfacial redox reaction based on β-AgVO(3) nanowires. The β-AgVO(3) core and two distinct layers can be clearly observed in single triaxial nanowire. Fourier transformed infrared spectroscopic and energy dispersive X-ray spectroscopic investigations indicate that the outermost layer is PANI and the middle layer is Ag(x)VO((2.5+0.5x)) (x < 1), which may result from the redox reaction of Ag(+) and aniline monomers at the interface. The presence of the Ag particle in a transmission electron microscopy image confirms the occurrence of the redox reaction. The triaxial nanowires exhibit enhanced electrochemical performance. This method is shown to be an effective and facile technique for improving the electrochemical performance and stability of nanowire electrodes for applications in Li ion batteries.

Molybdenum oxide nanowires: synthesis & properties

Molybdenum oxide nanowires have been found to show promise in a diverse range of applications, ranging from electronics to energy storage and micromechanics. This review focuses on recent research on molybdenum oxide nanowires: from synthesis and device assembly to fundamental properties. The synthesis of molybdenum oxide nanowires will be reviewed, followed by a discussion of recent progress on molybdenum oxide nanowire based devices and an examination of their properties. Finally, we conclude by considering future developments.

Three-dimensional graphene framework with ultra-high sulfur content for a robust lithium–sulfur battery

Lithium–sulfur batteries can deliver significantly higher specific capacity than standard lithium ion batteries, and represent the next generation of energy storage devices for both electric vehicles and mobile devices. However, the lithium–sulfur technology today is plagued with numerous challenges, including poor sulfur conductivity, large volumetric expansion, severe polysulfide shuttling and low sulfur utilization, which prevent its wide-spread adoption in the energy storage industry. Here we report a freestanding three-dimensional (3D) graphene framework for highly efficient loading of sulfur particles and creating a high capacity sulfur cathode. Using a one-pot synthesis method, we show a mechanically robust graphene–sulfur composite can be prepared with the highest sulfur weight content (90% sulfur) reported to date, and can be directly used as the sulfur cathode without additional binders or conductive additives. The graphene–sulfur composite features a highly interconnected graphene network ensuring excellent conductivity and a 3D porous structure allowing efficient ion transport and accommodating large volume expansion. Additionally, the 3D graphene framework can also function as an effective encapsulation layer to retard the polysulfide shuttling effect, thus enabling a highly robust sulfur cathode. Electrochemical studies show that such composite can deliver a highest capacity of 96 mAh·g–1, a record high number achieved for all sulfur cathodes reported to date when normalized by the total mass of the entire electrode. Our studies demonstrate that the 3D graphene framework represents an attractive scaffold material for a high performance lithium sulfur battery cathode, and could enable exciting opportunities for ultra-high capacity energy storage applications.

Graphene Oxide Templated Growth and Superior Lithium Storage Performance of Novel Hierarchical Co2V2O7 Nanosheets

Hierarchical Co2V2O7 nanosheets consisted of interconnected nanoparticles are synthesized by a facile method using graphene oxide as the template. The electrochemical reaction mechanism of the Co2V2O7 nanosheets is thoroughly investigated by in situ XRD and ex situ TEM. The initial Co2V2O7 transforms into CoO nanoparticles and vanadium oxides in the first cycle, and the following reversible conversion reaction mainly occurs between CoO and Co and lithiation/delithiation of the vanadium oxides. The Co2V2O7 nanosheet displays a high reversible capacity (962 mAh/g at 0.5 A/g) and remarkable high rate capability. When cycled at 5.0 A/g, a reversible capacity of 441 mAh/g can be retained after 900 cycles. The stable high capacity and excellent rate capability make the hierarchical Co2V2O7 nanosheets a promising anode material for lithium-ion batteries.

Mesoporous VO2 nanowires with excellent cycling stability and enhanced rate capability for lithium batteries

To combine the merits of the one-dimensional structure and the porous structure, mesoporous VO2 nanowires have been designed and reported for the first time. Excellent cycling stability and enhanced rate performance are obtained and may be attributed to the mesoporous nanowires, realizing both high surface area for more active sites and facile stress relaxation resulting in excellent structure stability. Our results demonstrate that the mesoporous nanowires are favourable for high-rate and long-life lithium batteries.

An electrospun hierarchical LiV3O8 nanowire-in-network for high-rate and long-life lithium batteries

Structural and morphological control of the LiV3O8 material has a significant impact on its electrochemical performance. In order to obtain a favorable structure, a hierarchical LiV3O8 nanowire-in-network is designed and constructed by electrospinning through a polymer crosslinking strategy. The crosslinking effect between poly(vinyl alcohol) (PVA) and poly(ethylene oxide) (PEO) not only benefits electrospinning, but also realizes a mild multi-step degradation process during calcination. Based on temperature-dependent experiments and thermogravimetric (TG) analysis, the function of polymer blends and the formation mechanism of the structure are discussed in detail. As a cathode for lithium batteries, LiV3O8 exhibits a high initial capacity of 320.6 mA h g−1 at 100 mA g−1 and a high-rate capacity of 202.8 mA h g−1 at 2000 mA g−1. This remarkable performance is attributed to its unique structure, which provides a large effective contact area, low charge transfer resistance, and improved structural stability. Our work indicates that the hierarchical LiV3O8 nanowire-in-network material is a promising cathode for use in high-rate and long-life rechargeable lithium batteries.

Hollow spherical LiNi0.5Mn1.5O4 built from polyhedra with high-rate performance via carbon nanotube modification

Lithium nickel manganese oxide spinel (LiNi0.5Mn1.5O4, LNMO) has attracted much attention as the cathode material for rechargeable lithium-ion batteries due to its high energy density and low cost. However, the short cycle life and poor high-rate capability hinder its commercialization. In this study, we synthesized hollow spherical LNMO built from polyhedral particles. The LNMO hollow structure guarantees sufficient contact with electrolyte and rapid diffusion of lithium ions. To enhance the conductivity, we use carbon nanotubes (CNTs) to modify the surface of the cathode. After CNT modification, the LNMO hollow structure manifests outstanding cycling stability and high-rate capability. It delivers a discharge capacity of 127 mA h g−1 at 5 C, maintaining 104 mA h g−1 after 500 cycles. Even at a high rate of 20 C, a capacity of 121 mA h g−1 can be obtained. The excellent electrochemical performance is ascribed to the unique structure and the enhanced conductivity through CNT modification. It is demonstrated that the CNT-modified hollow spherical LNMO is a promising cathode for lithium ion batteries.摘要本文通过调节烧结温度设计构筑了一种纳米多面体颗粒堆积的中空球状LiNi0.5Mn1.5O4材料, 并进一步通过碳纳米管(CNT)的改性来提高材料的循环性能和高倍率性能. 纳米中空结构不仅减少了锂离子的扩散路径, 也保证了电解液和正极材料的充分接触, 三维网状CNT的 改性提高了材料的电子导电率, 从而明显改善了材料的循环和高倍率性能. 最终得到的LNMO-850/CNT材料在5 C的电流密度下初始容量为 127 mA h g−1, 500次循环后容量保持在104 mA h g−1. 而在20 C的高电流密度下容量仍达到121 mA h g−1, 体现了材料优异的循环和高倍率性能.