LiFePO4正极材料存在的问题及改进方法

锂离子电池正极材料正在向着高比能量、长寿命、低成本、环境友好的方向发展,而具有橄榄石结构的LiFePO4正极材料以其结构稳定、成本低、无污染等优点成为21世纪最理想的绿色电源,但自身也存在缺点.综述了锂离子电池正极材料LiFePO4的发展状况,从物质结构与电化学特性出发指出了其存在的问题.重点介绍了国内外为改进LiFePO4正极材料的综合性能而进行的有关制备方法以及对其改性的研究.     

GSH-assisted hydrothermal synthesis of MnxCd1−xS solid solution hollow spheres and their application in photocatalytic degradation

A series of Mn_xCd_1−xS (MCS) solid solutions hollow spheres (x=0.0, 0.20, 0.33, 0.50 and 0.67) have been synthesized with the assistance of l-Glutathione (GSH) by a simple hydrothermal route for the first time. Different characterization techniques, including X-Ray diffraction (XRD), atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller surface area (BET), UV–vis and diffuse reflectance spectra (DRS) are performed to investigate the structural and optical properties of the as-prepared samples. The experiment of rhodamine B (RhB) decoloration indicates that all the MCS samples show higher photo-catalytic activities than commercial CdS under visible light irradiation. Among them, the Mn_0.33Cd_0.67S exhibits the highest photo-catalytic activity. The superior photo-catalytic activity of MCS samples may be attributed predominantly to the synergistic effect of the appropriate band-gap structure as well as the special hollow spherical morphology which makes MCS samples have the ability to harvest exciting visible-light due to multiple scattering within the interior space. Furthermore, the Mn_0.33Cd_0.67S shows well stability, the photo-catalytic activities do not decrease significantly after six recycles. The work may open a novel strategy to fabricate multi-component chalcogenide solid solutions hollow spheres.     

Uniform Bi2S3 nanorods-assembled hollow spheres with excellent electrochemical hydrogen storage abilities

Hierarchical Bi₂S₃ hollow spheres have been synthesized by a facile solvothermal process in the presence of sodium tartrate. The hollow spheres are composed of numerous ultrathin nanorods with the average diameter of 15 nm. Based on the time dependent electron microscope observations, the formation mechanism of such hierarchical structures has been proposed as a sodium tartrate directed self-assembled process and oriented attachement mechanism. The morphology and size of the subunits can be controlled by adjusting the amount of sodium tartrate. The Nitrogen adsorption-desorption measurements suggest that mesopores exist in these hollow spheres. The as-derived Bi₂S₃ hollow spheres exhibit excellent electrochemical hydrogen storage properties.     

A TEM study of morphological and structural degradation phenomena in LiFePO4‐CB cathodes

LiFePO₄‐based cathodes suffer from various degradation mechanisms, which influences the battery performance. In this paper, morphological and structural degradation phenomena in laboratory cathodes made of LiFePO₄ mixed with carbon black (CB) in a 1 mol/L LiPF₆ in EC : DMC (1:1 by weight) electrolyte are investigated by transmission electron microscopy at various preparation, assembling, storage, and cycling stages. High‐resolution transmission electron microscopy imaging shows that continuous SEI layers are formed on the LiFePO₄ particles and that both storage and cycling affect the formation. Additionally, loss of CB crystallinity, CB aggregation, and agglomeration is observed. Charge–discharge curves and impedance spectra measured during cycling confirm that these degradation mechanisms reduce the cathode conductivity and capacity. Copyright © 2016 John Wiley & Sons, Ltd.     

关于大型铝电解槽新型节能技术优化的探讨

阐述了具有新型结构的铝电解槽节能技术,并以特定电解槽为模型进行了计算,分析了这些节能技术应用的可行性。     

Simulation study on horizontal continuous casting process of copper hollow billet under rotating electromagnetic stirring Part 1—model description and primary results

In this paper, a comprehensive three-dimensional mathematical model is built to investigate the effect of rotating electromagnetic stirring on solidification process of copper hollow billet during horizontal continuous casting. The finite element package ANSYS and the commercial finite volume package FLUENT are employed for simulating electromagnetic field and thermal flow field respectively. The Lorenz force and Joule heat are transferred between them with a special data communication method. The model involves the solution of Maxwell equations, Navier—Stokes equations and energy equation for the turbulence characteristics κ and ?. The measured magnetic flux density is used for validating the proposed model. The simulated results show that rotating electromagnetic stirring causes a swirling motion in the hollow billet and makes the temperature field uniform. In the present study, the temperature gradient decreases from 748 to 196 K m^?1, and the sump depth is reduced from 48·8 to 29·0 mm.     

Solution blow spun nickel oxide/carbon nanocomposite hollow fibres as an efficient oxygen evolution reaction electrocatalyst

The development of efficient electrocatalysts for slow reaction of the oxygen evolution reaction (OER) is fundamental for viability of the electrochemical water splitting technologies. Here we report for the first time the synthesis of NiO/carbon hollow fibres (NiO-HF) by the Solution Blow Spinning (SBS) technique, and a study of their catalytic activity towards the OER in alkaline medium. The hollow fibres were obtained with ca. 300 nm in diameter consisting of agglomerated NiO nanoparticles with an average size of 50 nm which is close to the tubular wall thickness. The formation mechanism of the hollow structure was discussed. It was revealed that the carbon from polyenic branch of polyvinylpyrrolidone (PVP) resists the firing treatment and acts as an agglomerating agent, thus ensuring a conductive and percolating path between NiO nanoparticles along the fibres. A battery of electrochemical tests of NiO-HF supported by commercial Ni foam reveals excellent electrochemical activity for OER in 1 M KOH, in comparison with reference NiO nanoparticles (NiO-NP, diameter ca. 23 nm). NiO-HF attains an overpotential of 340 mV vs. RHE at a current density of 10 mA cm⁻², which is amongst the lowest values reported in the literature for undoped NiO. Chronopotentiometry reveals stable NiO-HF electrodes over 15 h under an electrolysis current of 25 mA cm⁻². Microscopic analysis shows that the fibrillar morphology is completely preserved after the electrolysis test. The remarkable performance of the NiO-HF catalyst is ascribed to the enhanced electronic conductivity resulting from the interpenetrating NiO-HF/carbon microstructure.     

High current density Sc2O3-W matrix dispenser cathode

Sc2O3-W matrix dispenser cathodes have been prepared by powder metallurgy method and tested in Pierce electron guns.The emission current density can reach 72 A/cm2 at 900C and over 100 A/cm2 can be achieved at a temperature higher than 950C.The emission improves and then keeps stable with time throughout the life testing period of 330 h at a continuous loading of 88 A/cm2pulsed current density with a pulse width of 10μs and duty cycle of 0.2%.The cathode surface is covered by a semiconductor multilayer composed of Ba,Sc and O.The emission behavior of the cathode can be explained by a semiconductor model.     

Jute and hollow conjugated polyester composites for outdoor & indoor insulation applications

The research work aims at investigating the fitness of jute and hollow conjugated polyester (HCP) composites for indoor and outdoor applications. Limiting oxygen value index, natural weathering exposure was done on four optimized composite structures; i) sandwich structure composite (A); ii) blended non-woven structure composite (B); iii) multiple layers with 5% of low melt polyester added composite (C); (iv) multiple layers of non-woven stitched composite (D) were produced. Their tensile strength, strain at break, and Young’s modulus values were evaluated both before and after the coating of acrylic-based silicon emulsion (ASE). From the experimental results, it is suggested that sample A can be used for an interior trim, sample B can be a base material for interior designing, sample C can replace the usage of wood, plastics, metals, and alloys in hardware applicationsand sample D can be used in interiors as an insulation material in commercial buildings for the purpose of internal cooling or heating.