Rongjian Xue

Lithium ion conduction in polymer electrolytes based on PAN

Abstract Polymer electrolytes based on polyacrylonitrile (PAN) with various plasticizers have been synthesized. Their electrical conductivities determined by AC impedance spectra are higher than 1 × 10−3 S · cm−1 at room temperature. IR and Raman spectra gave evidence of the interactions among PAN, plasticizer and lithium salt.

The mechanism of lithium ion transport in polyacrylonitrile-based polymer electrolytes

Abstract A dozen polyacrylonitrile (PAN)-based polymer electrolytes containing various plasticizers, have shown ionic conductivities higher than 1 × 10−3 S cm−1 at room temperature. In order to explain the high ionic conduction in these systems, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), Raman scattering and infrared (IR) spectra have been measured systematically. Based on these results, a mechanism of Li+ ion transport in PAN-based polymer electrolytes has been suggested. There are three kinds of Li+ ions: one in the gel state of PAN, the other in solid PAN and the third in the plasticizer. The high ionic conduction is mainly caused by the Li+ ions in the gel state. These Li+ ions are coupled with the CN group in PAN and the CO group in the plasticizer. The Li+ ions can jump from one position to the next along a chain, while moving together with the chain.

Microwave synthesis of LiCoO2 cathode materials

LiCoO2 is synthesized by microwave heating. It has high capacity and good cycleability. The advantages of microwave synthesis are: (i) the calcination process is very fast; (ii) the synthesized powders have small and uniform grains; (iv) the synthesis temperature can be lower, and (iv) the lithium oxide loss is smaller

Chemical and crystalline structure characterizations of polyfurfuryl alcohol pyrolyzed at 600 °C

Polyfurfuryl alcohol (PFA) is pyrolyzed at 600 degrees C for different lengths of heat-treatment time (HT). Systematic analysis by X-ray diffraction, infrared (IR) and Raman spectroscopy as well as elemental analysis indicates that the microstructure of pyrolytic carbon from PFA is very sensitive to HT at 600 degrees C. Therefore, by controlling HT at 600 degrees C, microcrystalline particles of carbon with different hydrogen contents and different crystallite sizes can be obtained

Spectroscopic investigation of interactions among components and ion transport mechanism in polyacrylonitrile based electrolytes

Raman, infrared (IR), fluorescence, X-ray photoelectron (XPS), and nuclear magnetic resonance (NMR) spectra of various combinations of the components of the polyacrylonitrile (PAN)-based electrolytes have been studied, it is found that the so-called composite- or mixed-phase polymer electrolytes are not simple mixtures of electrolytic salt, plasticizer and polymer; instead there are strong interactions between each two of the components of the electrolytes and strong competitions between the plasticizer and PAN to associate with the Li+ ions though different systems may show different interaction characteristics. By analyzing the important roles of the plasticizer, a possible mechanism of the ion transport in the PAN-based polymer electrolyte is proposed

Investigation of the position of Li+ ions in a polyacrylonitrile-based electrolyte by Raman and infrared spectroscopy

The Raman spectra of polyacrylonitrile (PAN) and/or lithium perchlorate (LiClO4) complex containing plasticizer ethylene carbonate and the infrared spectra of the polymer electrolytes with different mass ratios of PAN to LiClO4 have been studied. It has been found that the lithium ions strongly interact with the C=N groups of PAN. However, at the ordinarily used content, say, the concentration of Li+ ions is as low as 5%, because of the high intensity of the characteristic vibration of the C=N group of PAN, it is very difficult to observe the interaction between the ions and the molecules. When the content of LiClO4 is raised to a certain extent, this interaction can be detected by way of Raman and IR spectroscopy. In both the Raman and IR spectra of the system of EC/PAN/LiClO4 with various mass ratios of PAN and LiClO4, a striking shoulder was observed at about 2270 cm(-1). By comparing the spectra of the system with that of EC/PAN and EC/LiClO4, the new shoulder was assigned to the interaction between Lit ions and the C=N groups of the PAN molecules. Copyright (C) 1996 Elsevier Science Ltd.

Infrared spectroscopic study of the interaction between lithium salt LiClO4 and the plasticizer ethylene carbonate in the polyacrylonitrile-based electrolyte

Abstract The infrared (IR) spectra of ethylene carbonate (EC) containing different contents of lithium perchlorate (LiClO 4 ) have been measured and analyzed. It is found that, with the increase of the LiClO 4 content in the solution, both the vibrational frequencies and the relative intensities of the bands related to the ring structure and to the CO group of EC molecule are changed. The data have shown that there is a rather strong interaction between the Li + ion and the EC molecule. The interactions between the Li + ions and the EC molecules mainly occur on the CO group of the molecules. In the meantime, the structure of the ClO 4 − anion is also affected by the EC molecules, forming solvent-shared ion pairs, Li + ECClO 4 .

Characterization of flow units in metallic glass through structural relaxations

We characterize the evolution of flow units associated with the flow “defects” in metallic glass by monitoring the fictive temperature change of a typical metallic glass upon isothermal annealing below its glass transition temperature. The correlations between the fictive temperature Tf, enthalpy change, and the concentration of flow units have been obtained. Such correlations help in understanding the evolution process of flow units, structural feature, and structural relaxation behaviors in metallic glasses, and can rationalize effects of the cooling rate, aging, and annealing on properties and structure of metallic glasses.

Dispersion effects of Raman lines in carbons

Raman spectra of highly oriented pyrolytic graphite (HOPG), natural polycrystalline graphite (PCG), high pressure graphite (HPG), and low-temperature pyrolyzed polyfurfuryl alcohol (PFA) have been measured. Comparing the Raman spectra of each sample illuminated with laser beams of 488.0 nm and 1064.0 nm wavelengths, respectively, unambiguous dispersion effects have been observed for the D′-line in HOPG and in other forms of PCG as well as for their D lines. Comparisons of the intensity ratios of the D′ line to the D line (ID′/ID) of HOPG and polycrystalline indicate that the dispersion effects of the D′ line and the D line may have the same physical origin. In addition, it has also been observed that the G-line position of low-temperature pyrolyzed PFA is sensitive to the excitation wavelength while that of HOPG, PCG, and HPG is not. This phenomenon is attributed to the nanometer size of the microcrystalline graphites by analyzing the factors that may induce such a dispersion effect.

Ion association and solvation studies of LiClO4 ethylene carbonate electrolyte by Raman and infrared spectroscopy

Dispersion strengthened (DS) Cu-Al25 alloy containing small Al2O3 particles (similar to 4 nm in diameter) was irradiated by 300 keV Cu+ ion to doses of 10 dpa and 30 dpa with a displacement rate of 3.7 x 10(-2) dpa/s at room temperature, which simulates the effects of high energy primary knock-on atoms (PKA) produced by 14 MeV neutrons. Microstructural evolution was investigated by transmission electron microscopy (TEM). Selected area diffraction (SAD) was used to study the phase stability of alumina under irradiation. The defect cluster structure formed by irradiation was investigated by dynamic two-beam techniques. Small particles of Al2O3 were dissolved under ion irradiation with increasing fluences. A large number of small Frank vacancy and interstitial dislocation loops (similar to 5 nm in diameter) with different Burgers vectors of a/3[1 1 1] are produced by ion irradiation. At the region adjacent to the irradiation surface the number of vacancy loops was greater than that of interstitial ones. This result is in good agreement with the computer simulation results