E. Sominski

Development and testing of nanomaterials for rechargeable lithium batteries

Abstract The use of nanoparticles in composite electrodes for Li batteries may have considerable kinetic advantages due to the reduction of the diffusion length for lithium insertion in the active mass, and also because of the reduction of the overall charge transfer resistance of the electrodes. We report herein on the synthesis of various types of nanomaterials for rechargeable lithium batteries and their testing as active mass in anodes and cathodes. These include SnO, VO x , Li x MnO 2 , and various types of carbon nanotubes. Sonochemistry was applied for the synthesis of part of the nanophases. The tools for this study included X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and standard electrochemical techniques (CV, SSCV, chronopotentiometry and impedance spectroscopy).

Materials synthesis and characterization of 8YSZ nanomaterials for the fabrication of electrolyte membranes in solid oxide fuel cells

Two different nanosized materials were synthesized by two preparation methods, namely a sonochemical technique and a spray pyrolysis process. The powder properties, the sintering behavior and the resulting crystallinity with respect to their utilisation for solid oxide fuel cell electrolytes were investigated. While the spray pyrolysis provides crystallized powder without any organic residue, the sonochemical powder is amorphous with some organic residue. Crystallization begins in the 400–500 °C temperature domain. The particle sizes vary between 10 and 50 nm for the sonochemical powder and between 50 nm and 1 μm for the spray pyrolysis powder, as determined by SEM analyses. Crystal growth of both powders starts between 800 and 1000 °C. After heating and sintering at 1300 °C the resulting grain sizes of the spray pyrolysis powder are 5 times larger than those of the sonochemical powder (about 250 nm and 1.2 μm, respectively). Additionally, the maximum rate of grain growth for the spray-pyrolysed material at 97 nm/h is even higher compared with 22 nm/h for the sonochemical powder.

Microwave-assisted solid-state synthesis and characterization of intermetallic compounds of Li3Bi and Li3Sb

Li3Bi and Li3Sb are two types of intermetallic lithium alloys, which were prepared for the first time by a microwave-assisted solid-state reaction. They were characterized by PXRD and SEM techniques. Pure phases of Li3Bi and Li3Sb were obtained after only 2 min and 1 min irradiation at 80% microwave power, respectively. The microwave method was found to be simple, fast and efficient for the preparation of these compounds. The oxidization processes of the two intermetallic lithium alloys in air were investigated. After exposure of the two intermetallic compounds to air for 5 hours only the corresponding Bi and Sb were detected by XRD analyses, the Li metal having been converted to amorphous Li2O. SEM observations show that the products are homogeneous, meaning that Bi and Sb are homogeneously dispersed in the amorphous products. The oxidized products may be potential composite anode materials for Li ion batteries.

Magnetic Properties of La

AC and DC magnetic measurements in temperature interval 5-300 K and at external magnetic field Hles 5 T were employed to probe and compare magnetic ordering in bulk and nanometer-sized (15plusmn2 nm) La0.7Ca0.3MnO3 single crystals. The respective Curie temperatures (TC)~239 K and 233 K, close to each other are observed in bulk and nano samples. While, their low T spontaneous magnetizations are strongly different, being about 3.6 and 1.2 muB/f.u., respectively. AC susceptibility (chi) of a bulk sample, measured at Hdc=0, shows a maximum of chi(T) at T~TC. In a contrast, chi(T) of the nano-sample demonstrates a broad maximum far below its TC. In the nano-sample both real and imaginary parts of chi are frequency dependent within the 5-280 K range. In a contrary, the frequency dependence is observed only for imaginary part of chi in bulk crystal. It is concluded that the similar ferromagnetic ground state exists in both considered samples; however, it is strongly frustrated in agglomerated nano particles due to surface magnetic disorder and interparticle interactions.

_{0.7}

ac and dc magnetic measurements have been employed to probe and compare magnetic ordering in bulk and nanometer-sized La0.9Ca0.1MnO3 single crystals. About the same cationic content was determined in both types of the samples. However, the magnetic ground state of the bulk crystal is characterized by a complex mixture of antiferromagnetically and ferromagnetically ordered phases, while the ground state of the nanosample seems to be ferromagnetic and coexisting with the superparamagnetic state at T<240K. The results are discussed in terms of the different randomness of indirect ferromagnetic exchange interactions mediated by the bound holes.

Ca

A sonochemical process for the fabrication of the mesoporous composite NiO/yttria stabilized zirconia (YSZ) is described. Its surface area after the extraction of the surfactant is 193 m 2 /g for a sample containing 40 atom-% Ni. The main advantages of the sonochemical method, as compared with previous works, are the short reaction time (6 h) and that there is no requirement for the glycolation of the nickel, yttrium, and zirconium ions. The reduction of NiO/YSZ to the corresponding Ni/YSZ is also reported. 2003 Elsevier Science Inc. All rights reserved.

_{0.3}

High quality MCM-41 silica with thick walls and a very narrow distribution of mesopore size has been synthesized in a relatively short time via ultrasound radiation.

MnO

The data on X-band ferromagnetic resonance (FMR) in the half and electron-doped La0.5Ca0.5MnO3 (Ca0.5) and La0.4Ca0.6MnO3 (Ca0.6) nano-crystals and bulk ceramics are reported. The FMR data for considered nano-samples appeared to be strongly different, reflecting a difference in their magnetic/electronic order. An enhancement of the FMR signal intensities is observed in both nano Ca0.5 and Ca0.6 as compared to those in bulk. The peak intensity of such signal in nano Ca0.5 exceeds about two orders of magnitude the corresponding value in nano Ca0.6. This finding evidences on the respective ferromagnetic like and charge ordered antiferromagnetic ground states in Ca0.5 and Ca0.6.

_{3}

To explore the size effect in electron-doped La0.4Ca0.6MnO3 (LCMO) compound, dc magnetic measurements and electron magnetic resonance were carried out with bulk and nano-grained LCMO in temperature ranges 5 K les T les 350 K and 5 K les T les 600 K, respectively. It appears that the antiferromagnetic, charge ordered state remains stable upon the reduction of the samples size down to nanometer scale. However, the low-temperature ferromagnetic (FM) component enhances in nano-grained LCMO as compared to its bulk counterpart, supposedly due to strong surface and inter-grain interaction effects. FM correlations in bulk and nano crystals are strong at paramagnetic (PM) state, which seems to be an electron-doping effect. The domination of ion-ion spin relaxation mechanism in PM state and drastic fading of the FM correlations upon cooling means that the doped electrons are localized in both bulk and nano-grained LCMO. The notable influence of the oxygen stoichiometry on magnetic ordering in LCMO, revealed in this work, may explain the contradictive data on the magnetic state of nano-crystalline LCMO reported in the literature.