Cobalt oxide thin films for high capacity and stable Li-ion battery anode

Journal of Solid State Electrochemistry - Here, we report reactive DC-sputter deposited Co3O4 thin films as a promising and stable Li-ion battery anode. Thin films were deposited on stainless steel...     

Electrosprayed NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles for long cycle life and high-power Li-ion battery anode

Electrospraying-based synthesis of NiCo₂O₄ (NCO-ES) nanoparticles that exhibit long cycle life and high rate capability is reported. The results are compared with a conventionally prepared NiCo₂O₄ sample by direct annealing (NCO-DA). The structure and morphology of NCO-ES and NCO-DA nanoparticles have been characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy to confirm the size, morphology, structure, and surface chemistry of the as-prepared samples. Electrochemical testing established that the NCO-ES sample displayed enhanced Li-ion storage performance. The NCO-ES delivered a discharge capacity of almost 370 mAh/g at the end of 50 cycles at 1C rate (890 mA/g) while only 180 mAh/g was retained for the NCO-DA sample at the same condition. At a high rate of 5C (4450 mA/g), NCO-ES electrodes delivered a stabilized specific capacity of 225 mAh/g with almost 100% Coulombic efficiency over 1000 cycles. Its rate capability and cycle life were found to be superior to NCO-DA electrodes. The nanoscale grain boundaries in the NCO-ES sample enhanced the lithium-ion diffusion and enabled high rate capability. The impedance analysis at different stages of lithiation/delithiation indicates a lower impedance and better kinetics as one of the reasons for better performance of the NCO-ES sample.     

Spray pyrolysis-deposited TiO<Subscript>2</Subscript> thin films as high-performance lithium ion battery anodes

Focusing on additive-free electrodes, thin films are of typical interest as electrodes for lithium ion battery application. Herein, we report the fabrication of TiO₂ thin films by spray pyrolysis deposition technique. X-ray diffraction and transmission electron microscopic analysis confirms the formation of anatase TiO₂. Electrochemical evaluation of these sub-micron TiO₂ thin films exhibits high-rate performance and long cycling stability. At 1C rate (1C?=?335 mA/g), the electrode delivered discharge capacity of 247 mAh/g allowing about 0.74 lithium into the structure. The electrodes also delivered specific capacities of 122 and 72 mAh/g at 10 and 30C rates, respectively. Without conductive additives, this excellent performance can be attributed to the nanosize effect of TiO₂ particles combined with the uniform porous architecture of the electrode. Upon cycling at high rates (10 and 30C), the electrode exhibited excellent cycling stability and retention, specifically only <?0.6% capacity loss per cycle over 2500 cycles.     

Highly Selective and Sensitive Aggregation-Induced Emission of Fluorescein-Coated Metal Oxide Nanoparticles

We report the synthesis, characterization, and photophysical properties of novel metal oxide nanoparticles (NPs) coated with specially designed fluorescein substituents which are capped with electron-withdrawing groups. The fluorescein-coated nanoparticles were synthesized in excellent yields, and their structures were confirmed using various advanced spectroscopic, instrumental, and surface analysis techniques, revealing the formation of the target functionalized nanoparticles (FNPs) which show superior chemical and thermal stabilities. In addition, the photophysical properties of the FNPs were examined using UV-visible absorption and fluorescence spectroscopy. These latter techniques disclosed aggregation-induced emission (AIE) properties for most of the target FNPs, namely those which are soluble in common organic solvents at selective concentration ranges of water fractions in the solvent mixture.     

Chemoselective Selenium Dioxide Oxidation of 1,4-Adducts Derived from Substituted Arylidene Acetophenones

The chemoselective reactions of selenium dioxide with differently substituted adducts generated by 1,4-addition on benzylidene acetophenone are described. This reaction has been shown to be dependent on the nature of the substituent present, leading to different products by α-oxidation/α-oxidation followed by dehydrogenation/dehydrogenation, enolization, and cyclization.     

High-voltage electrophoretic deposition for vertically aligned forests of one-dimensional nanoparticles

Deposition of aligned forests of 1D nanoparticles (carbon nanotubes and MnO(2) nanorods) on conductive, including flexible and transparent, substrates has been achieved at room temperature. The process, named high-voltage electrophoretic deposition (HVEPD), has been enabled by three key elements: high deposition voltage for alignment, low dispersion concentration of the nanoparticles to avoid aggregation, and simultaneous formation of a holding layer by electrodeposition. The effects of key parameters are investigated. The alignment on the vertical direction has been revealed by scanning electron microscopy of the samples, their superhydrophobicity, electrochemical performance, and capability to electrically connect two separated electrodes. Compared with their randomly oriented counterparts, the aligned nanoforests showed higher electrochemical capacitance, lower electrical resistance, and the capability to achieve superhydrophobicity, implicating their potential in a broad range of applications.     

Estimating parameters from rotating ring disc electrode measurements

Rotating ring disc electrode (RRDE) experiments are a classic tool for investigating kinetics of electrochemical reactions. Several standardized methods exist for extracting transport parameters and reaction rate constants using RRDE measurements. In this work, we compare some approximate solutions to the convective diffusion used popularly in the literature to a rigorous numerical solution of the Nernst–Planck equations coupled to the three dimensional flow problem. In light of these computational advancements, we explore design aspects of the RRDE that will help improve sensitivity of our parameter estimation procedure to experimental data. We use the oxygen reduction in acidic media involving three charge transfer reactions and a chemical reaction as an example, and identify ways to isolate reaction currents for the individual processes in order to accurately estimate the exchange current densities.     

In situ growth of LiFePO4 nanorod arrays under hydrothermal condition

A novel in situ combinatorial method has been developed to fabricate LiFePO₄ nanorod arrays, during which anodized alumina oxide (AAO) was employed as the template and ethylene glycol/water medium is used to ensure mass transportation rates of different chemicals to match each other. The samples were then characterized by X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDX). After being hydrothermally processed at 160 °C, the highly-crystallized LiFePO₄ arrays were directly obtained, which are composed of single crystal nanorods with a diameter of 200 nm and a length of 3 μm. The reported synthesis is simple, mild and energy-efficient. A noteworthy advantage over conventional sol–gel–template methods is the elimination of high-temperature annealing.     

Microstructure control of MnO2/CNT hybrids under in-situ hydrothermal conditions

In this work, single-crystalline MnO₂ nanoparticles were directly grown on the surface of multi-walled carbon nanotubes (CNTs) homogeneously under in-situ hydrothermal conditions, during which the CNTs were well dispersed in aqueous solution with the aid of dodecyl benzene sulphonic acid sodium (SDBS). This stable suspension ensures the continuous deposition of the MnO₂ nanocrystals. It was found that the MnO₂/CNTs nanocomposites formed in the presence of CNTs, but the MnO₂ nanowires formed without CNTs under the same hydrothermal conditions. Moreover, the as-synthesized MnO₂/CNTs sample showed a high specific capacity and cycling stability, which was ascribed to its highly-homogeneous hybrid nanostructure. This homogeneous MnO₂/CNTs nanocomposite is shown to be able to take full advantages of both the high capacity of MnO₂ and the high electron conductivity of CNTs by integrating them homogeneously. This homogeneous hybrid nanostructure is a promising electrode material for energy storage/conversion devices with excellent performances.     

Self-assembly of LiFePO4 nanodendrites in a novel system of ethylene glycol–water

In this work, a novel system of ethylene glycol/water (EG/W) was employed to synthesize LiFePO₄, in which dodecyl benzene sulphonic acid sodium (SDBS) was used as soft template to control particle morphology. The samples were characterized by X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX). The LiFePO₄ sample obtained by the reported method displays interesting hierarchical nanostructure (i.e. nanodendrites), which was constructed by nanorods of 3–5 μm in length and ∼50 nm in diameter. The EG/W ratio, amount of SDBS added, hydrothermal temperature and duration played important roles in the assembly of the hierarchical nanostructures. A formation mechanism was proposed and experimentally verified. It is concluded that the nanodendrites were formed due to the end-to-end self-assembly of nanorods. Compared to previously reported methods, the reported approach shows obvious advantages of one-step synthesis, environmental friendliness and low cost, to name a few. The nanodendrites as a cathode material have a higher capacity, compared with the other samples.