Materials Science Forum Vols. 743-744

Abstract: The effects of Fe addition on the precipitate characteristics and out-of-pile corrosion behavior of Zr-1Nb-xFe alloys, with x=0, 0.2 and 0.4 respectively, were investigated. The experimental results showed that the alloy with the composition of Zr-1Nb-0.4Fe had the best corrosion resistance and the alloy with the composition of Zr-1Nb-0.2Fe had the worst corrosion resistance. The relationship between the corrosion behavior and the microstructures including precipitate characteristics was discussed, and the elements contents, area fraction, as well as the mean diameter of the precipitate were analyzed. The β-Nb precipitate was found in Zr-1Nb alloy, both Zr (Nb,Fe)₂ precipitate and β-Nb precipitate were formed in Zr-1Nb-0.2Fe alloy, while only Zr (Nb,Fe)₂ precipitate was observed in Zr-1Nb-0.4Fe alloy. It has been found that the size of precipitates increased with the increasing of Fe content. This work indicated that the Fe content dominates the crystal structure, volume fraction and the element contents of the precipitate, which affect the corrosion resistance of Zr alloy.

Abstract: Graphite oxide (GO) is layered structure with functional groups such as hydroxyl, carboxyl and carbonyl between layers. Using GO as cathode active material allows lithium ions to enter the interior of cathode active material easily and the transformation of crystal form can also be obviated. GO has large amounts of surface area which enables cathode material to contact with liquid electrolyte directly, thereby direct and fast surface adsorption and reaction with lithium ions can be achieved. In this article, GO was prepared by modified Hummers method, characterized by XRD, IR, TG, and its electrochemical performance is studied as cathode active material. It is discovered that capacity can be dramatically improved and the cycle performance is excellent when GO is used as cathode material. The discharge capacity of first cycle can reach 480mAh/g at the current density 0.1A/g. The capacity is above 90% after 10 cycles.

Abstract: Li₄Ti₅O₁₂ thin film anodes were prepared successfully using pulsed laser deposition technique. The thin films were characterized by X-ray diffraction and environmental scanning electron microscopy. The effects of thickness and scan rate on the electrochemical properties of Li₄Ti₅O₁₂ thin film electrodes were discussed in detail. The thin film anodes deliver favorable capacity and excellent cycling performance. The discharge capacity maintains at 141 mAhg^-1 after 20 cycles at 1C charge-discharge rate for the thin film anodes deposited for 20 minutes. The charge-transfer resistances were also investigated by electrochemical impedance spectroscopy.

Abstract: To improve the controllability of the fabrication of carbon aerogels, the effects of the concentration of the reactant (RF%) on the structural properties of organic resorcinol formaldehyde (RF) gel and the effects of the carbonization temperature on nanostructure of carbon aerogels were discussed. The concentration of the reaction was turned from 5%,10%,20%,30%,40%,50%,55% and 60% to prepare the samples. The RF aerogels were carbonized at temperature of 700, 900 and 1050. The shrinkage and nitrogen gas adsorption were measured. Experimental results showed that the structural stability of the organic RF aerogel can be improved by decreasing the shrink in drying process and increasing the condensation of reactant in the starting solution to a certain value, such as 55%. The ordered pore size distribution of carbon aerogels with less structure defects is able to be produced through the effective particle fusing at the carbonization temperature as high as 1050.

Abstract: The problems such as poor oxidation resistant properties at high temperatures and abated thermal storage capacities after repeated thermal cycles still exist in heat storage alloys. In order to alleviate these problems, orthogonal experiment was used to design nine Al-Si-Mg-Cu alloys in this work. An SII TG/DTA6300 differential thermal analyzer was used to determine the heat storage properties of these alloys. After integrating a series of factors, Al-12Si-2Mg-15Cu alloy was selected as the heat storage alloy. The oxidation test of this alloy at the temperature of 650 °C for 300 h was carried out, and the oxidation kinetics curve was obtained. The results showed that the oxide film was of good protection. This alloy exhibited a good thermal stability in view of the latent heat of fusion decreased 3.53%, the initial phase transition temperature decreased 0.1 °C, and terminated phase transition temperature increased 3.1 °C after 150 times of thermal cycles. The photomicrograph was used to discuss the reasons of the performance changes of this alloy.

Abstract: Phase inversion of polymer solution by immersion-precipitation method was used to prepare porous hollow capsule nickel boride composite. The composite was used as a carrier for sodium borohydride, in which sodium borohydride was absorbed into the capsules or embedded in the capsules during the processing of capsules formation. The preparation method and adsorption property of the polymer capsules were studied. The effect of capsules structure on the storage capacity of sodium borohydride was investigated. The results showed that capsules prepared by 18wt% of PVDF-DMF solution with adding 15% PVP had the best adsorption capacity. While capsules prepared by PVA had better affinity to water, this made them easier to absorb sodium borohydride in the aqueous solution.

Abstract: nanosized FePO₄ and Fe_1-xCe_xPO₄ (x=0.02, 0.04, 0.08) cathode materials were synthesized by microemulsion method. The samples were prepared via a microemulsion system in a H₂O/cyclohexane/Triton x-100/n-butyl alcohol at different temperatures (30 , 45 , 50 , 60 ) and then sintered at 380 and 460 for 3 h. The thermal stability, structure and morphology were investigated by means of TG/DCS, X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and the electrochemical properties were characterized by cyclic voltammetry (CV) and galvanostatic charge and discharge tests. Results show that synthesis temperature has a great influence on the performances of FePO₄, and the sample synthesized at 45 shows the best performances with a diameter of about 20 nm and a high discharge initial specific capacity of 142mAh/g and retaining 123mAh/g after 20 cycles at 0.1 C. The Ce-doped FePO₄, Fe_1-xCe_xPO₄ (x=0.02, 0.04, 0.08), can effectively improve the electrochemical properties of FePO₄ cathode materials. The Fe_0.96Ce_0.04PO₄ exhibits an initial discharge capacity of 158.2mAh/g and retains 152mAh/g after 20 cycles at 0.1 C. Hence, Fe_0.96Ce_0.04PO₄ is a promising candidate for cathode materials of lithium ion batteries.

Abstract: In order to study the improvement mechanism of transition metal elements on Mg-based hydrogen storage alloys, especially for the structures and properties of hydrogen storage alloy Mg₂Ni, Ti and Zn substituted alloys Mg_2-mM_mNi,Mg₂Ni_1-nM_n (M=Ti and Zn, m, n=0.1667), and their hydrides Mg₂NiH₄,Mg_2-mM_mNiH₄,Mg₂Ni_1-nM_nH₄(M=Ti and Zn, m , n=0.125) have been investigated by first-principles. Through analyzing the results of the crystal structure, electron density distribution and density of states, the changes of structures and properties resulting from the adding of transition metal elements Ti and V of intermetallic Mg₂Ni and its hydride Mg₂NiH₄ were investigated. The results showed that the addition of transition metal elements can reduce the stability of the Mg₂Ni system to varying degrees and improve the dehydrogenation dynamics performance. Therefore, it may be considered that the substitution by transition metal elements in Mg-based hydrogen storage alloys is an effective technique to improve the thermodynamic behavior of hydrogenation/dehydrogenation in Mg-based hydrogen storage alloys (HSAs).

Abstract: Solid polymer electrolytes (SPEs) which were composed of poly (ethylene oxide) (PEO), poly (lithium acrylate) (PLiAA), and LiClO₄ were prepared in order to investigate the influence of LiClO₄ content on the ionic conductivity of the electrolyte. All of the membranes were investigated by XRD, DSC, and EIS, et.al. The dependence of SPEs conductivity on temperature was measured, and the maximum ionic conductivity is 5.88×10^-6 S/cm at 293 K for membrane which is composed of PEO+PLiAA+15wt% LiClO₄. The electrochemical stability window of the PEO+PLiAA+15wt% LiClO₄ is 4.75 V verse Li.