A. Deptula

A Novel Concept for the Synthesis of an Improved LiFePO4 Lithium Battery Cathode

This paper describes the synthesis and the properties of a kinetically improved LiFePO 4 cathode material. The novel aspect of the synthesis is based on a critical step involving the dispersion of metal (e.g., copper or silver) at a very low concentration (1 wt %). This metal addition does not affect the structure of the cathode but considerably improves its kinetics in terms of capacity delivery and cycle life. Such an enhancement of the electrochemical properties has been ascribed to a reduction of the particle size and to an increase of the bulk intra- and interparticle electronic conductivity of LiFePO 4 , both effects being promoted by the finely dispersed metal powders. This improved conductivity favors the response of LiFePO 4 , thus substantiating its interest as new cathode for advanced lithium ion batteries.

An electrochemical impedance spectroscopic study of the transport properties of LiNi0.75Co0.25O2

Analysis of impedance spectra taken at closely spaced bias potential values on LixNi0.75Co0.25O2 have been interpreted in terms of electronic and ionic transport properties of this electrode material. In the 0.9<x<1 range the material shows semi-conductive properties and the electronic conductivity dominates the transport. For x≤0.9, the properties change into those of a metal-like material in which the ionic conductivity becomes the limiting factor. The transition between these two limiting conditions clearly appears in the impedance spectra sequence. This transition is reversible since the same behaviour is observed during the lithium intercalation process as well as in the reverse lithium deintercalation process.

Preparation of spherical powders of hydroxyapatite by sol-gel process

Abstract Spherical powders of hydroxyapatite with particle diameters below 100 μm were prepared using the water extraction variant of the sol-gel process. A freshly prepared solution of calcium acetate and phosphoric acid (molar ratio Ca/P = 1.67) was emulsified in dehydrated 2-ethyl-1-hexanol. Drops of the emulsion were solidified by extraction of water with this solvent. The process was carried out continuously. The separated gel particles were calcined to hydroxyapatite particles with preservation of the spherical shape. This process was studied using differential thermal analysis, thermal gravimetric analysis, X-ray diffraction analysis and infrared spectroscopy. During thermal treatment, the formation of calcium carbonates is observed first. Above 400°C, the formation of hydroxyapatite starts and then at 580°C formation of carbonate hydroxyapatite starts. The last step, decomposition to hydroxyapatite, proceeds above 750°C.

Sintering of ZrO2 ‐ CeO2 Spherical Powders Prepared by a Water Extraction Variant of the Sol‐Gel Process

Fully and partially stabilized ZrO[sub 2] solid solutions are one of the most extensively studied solid oxide electrolyte systems due to the many practical applications of these materials. Spherical powders (with diameters 95% of the theoretical density) and showed both tetragonal and/or cubic X-ray phases. The bulk density values of these ceria-doped zirconia sintered pellets are much higher than those obtained for the CaO- or Y[sub 2]O[sub 3]- doped zirconia samples prepared by the same process.

Electrochemical characterization of a lithiated mixed nickel-cobalt oxide (LiNi0.5Co0.5O2) prepared by sol-gel process

Lithiated transition metal oxides having a layered structure and general formula LiMO2, have been extensively studied as positive electrode active materials for lithium or lithium-ion batteries. In particular, lithium nickel dioxide (LiNiO2) and lithium cobalt dioxide (LiCoO2) present a layered structure with high diffusion coefficients for the lithium ion. This latter property is very important in order to realize practical devices having high discharge rates. LiNiO2, compared with LiCoO2, has the advantage to be a cheaper material with a higher specific capacity for lithium cycling, but its stability upon cycling can be greatly influenced by the displacement of Ni ions from the Ni layers to the Li planes as the content in lithium is reduced over a certain value. Recently, solid solutions such as LiNixCo1−xO2 have been proposed to offer a compromise between stability, cost and capacity.In this work we have studied LiNi0.5Co0.5O2 prepared by the Complex Sol-Gel Process (CSGP). The advantage of this procedure toward the solid-state process is the high homogeneity in composition and in particle dimension of the synthesized compounds. The samples have been characterized electrochemically using chronopotentiometric, voltammetric and impedance measurements in liquid electrolyte. The results indicates that CSGP-synthesized LiNi0.5Co0.5O2 shows good cyclability (after 1000 cycles about 2/3 of the initial capacity can still be cycled) only if the anodic potential is limited to about 4.2 V. The quite low values of the specific capacity (∼70 mAh/g at C/1 charge-discharge rate) can be justified by the non-complete calcination reaction, as suggested by X-ray measurements. Kinetic properties have been evaluated by Electrochemical Impedance Spectroscopy measurements, which have shown quite high values for the lithium chemical diffusion coefficient (10−7÷10−8 cm2s−1) and its unexpected decrease as deintercalation proceeds from x=0.5 in LiNi0.5Co0.5O2.

Fabrication of Li2TiO3 spherical microparticles from TiCl4 by a classical, inorganic sol-gel route; characteristics and tritium release properties

Medium sized spherical particles of Li2TiO3 (with diameters below 100 μm) can be fabricated by a classical, inorganic sol-gel process, from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li : Ti molar ratio (MR) = 2; (5) thermal treatment at 1200°C. This temperature can be significantly lowered (to 750°C) by chemical treatment of chloride precursors (gels or starting solution TiCl4) with aq. ammonia or better with nitric acid. Tritium release from sol-gel made Li2TiO3 micro-spheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier.

Inorganic Sol-Gel Preparation of Medium Sized Microparticles of Li2TiO3 from TiCl4 as Tritium Breeding Material for Fusion Reactors

Microspheres of Li2TiO3 were fabricated by a classical, inorganic sol-gel process from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl and addition of LiOH; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li:Ti molar ratio MR = 2; (5) thermal treatment at 1200°C in order to receive chloride free product. This temperature can be significantly lowered (to 750°C) by dechlorination starting solution TiCl4 by chemical treatment of the with nitric acid to form of nitrate-stabilized titania sols. Tritium release from sol-gel made Li2TiO3 microspheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier.

Thermal Conversion of Gels Prepared by the Complex Sol-Gel Process (CSGP) from Li+-Me2+-CH3COO−-Ascorbic Acid (ASC)-NH4+-OH−-H2O Systems to LiMn2O4 and LiNixCo1 − xO2

The spinel LiMn2O4 and layered oxides LiNixCo1 − xO2 (x = 1; 0.75; 0) have been prepared by Complex Sol-gel Process (CSGP). The appropriate sol compositions were obtained from acetate aqueous solution of metals containing ascorbic acid by alkalizing it with aqueous ammonia. Gels were produced from the systems by evaporation of water and other volatilies at elevated temperatures. A very intense foaming was observed during the heating at the temperatures higher than 140°C. To avoid foaming in the course of the final thermal treatment, a very long (lasting several days) soaking step was found necessary. However pretreated materials exhibit self-ignition at temperature range 320–500°C dependent on socking conditions. The dependence of self-ignition temperature on carbon content in bed as well as on specific surface has not been proved. Final thermal transformation of gel to solid was studied by TG, DTA, XRD, and IR methods. It was observed that final compounds are formed faster from precursors which did not contain Ni (e.g. LiMn2O4 and LiCoO2), while Li carbonate is not formed in these systems. In contrast, in Li-Ni(Co)-O the formation of Li(or Ni)CO3 was always proved. In addition, during the thermal treatment Ni species are partially reduced even to metallic phase. This effect evidently restrains the formation of pure layered oxides phase. Electrochemical properties of carbonate free compounds are definitely better than of those containing CO3.

Sol-gel process for preparation of YBa2Cu4O8 from acidic acetates/ammonia/ascorbic acid systems

YBa{sub 2}Cu{sub 4}O{sub x} sols were prepared by addition of ammonia to acidic acetate solutions of Y{sup 3+}, Ba{sup 2+}, and Cu{sup 2+}. Ascorbic acid was added to part of the sol. The resultant sols were gelled to a shard or a coating by evaporation at 60 C. Addition of ethanol to the sols facilitated formation of gel coatings, fabricated by a dipping technique, on Ag or glass or substrates. At 100 C, gels formed in the presence of ascorbic acid were perfectly amorphous, in contrast to crystalline acetate gels. The quality of coatings prepared from ascorbate gels was superior to that of acetate gel coatings.

Some aspects of thermal conversion of gels to YBCO and BSCCO superconductors. Removal of carbonates from intermediate phases

Abstract The thermal transformation of acetate derived gels: YBCO and BSCCO to respective superconductors has been studied using thermogravimetry, XRD and i.r. techniques. Formation of carbonates was observed during the thermal treatment of all the materials examined. Thermal decomposition of the carbonates turned out to be more difficult in the YBCO than in BSCCO compounds. Nevertheless the negative effect of carbonates on the formation of BSCCO phases has been observed. Removal of carbonates from intermediate phases by low-temperature treatment with nitric acid strongly accelerates formation of the 2223 BSCCO superconducting phase.