Key Engineering Materials Vol. 388

Abstract: Effects of lattice defects on cathode properties of LiMn2O4 synthesized at low temperatures were investigated. LiMn2O4 powders were synthesized by a sol-gel method. The specific capacities of LiMn2O4 decreased from 134 to 81 mAh g-1 with decreasing heating temperature from 750 to 200°C. X-ray absorption spectroscopy showed that a large amount of lattice defects such as cation vacancies existed and cation mixing occurred in LiMn2O4 calcined at low temperatures. It was found that the low specific capacities of LiMn2O4 calcined at low temperatures were attributed to these lattice defects.

Abstract: Electrochemical properties of LiFePO4/carbon composites with various carbon materials were investigated to achieve high-rate charge and discharge properties. LiFePO4/carbon composites were synthesized by a pyrolysis of a LiFePO4 precursor solution added with porous graphite or particulate carbon powders. The LiFePO4/porous-graphite composite had a microstructure in which LiFePO4 particles existed on carbon surface and within pores. The LiFePO4/particulate-carbon composite had a microstructure in which each carbon particle was covered with LiFePO4 fine particles. The LiFePO4/porous-graphite and the LiFePO4/particulate-carbon composite electrodes showed high discharge capacities of 69 and 30 mAh g-1 at a high current density of 4000 mA g-1. The high electronic conductivity in the LiFePO4/porous-graphite composite contributed to achieving the large discharge capacity at the high current density.

Abstract: The electrode properties of Ba0.5Sr0.5CoyFe1-yO3-δ {BSCF(5/5/10y/10(1-y))} on a Ce0.8Sm0.2O1.9 electrolyte were investigated. BSCF powders were synthesized by a solid-state reaction. The electronic conductivities of BSCFs increased with increasing Co content and BSCF(5/5/8/2) showed the highest conductivity of 38 S cm-1 at 600oC. The electrode resistance was measured on symmetric cells, BSCF/Ce0.8Sm0.2O1.9/BSCF, over the temperature range from 600oC to 800oC. The electrode resistances decreased with increasing Co content and BSCF(5/5/8/2) showed the lowest electrode resistance in the whole temperature range, having an electrode resistance of 0.62
cm2 at 600oC.

Abstract: Phase studies and ac-conductivity measurements were carried out in the compositions M0.8In0.2Li0.2P2O7 [MILP] (M=Sn, Zr, Ti). The bulk conductivities were of the order of ~10-5 Scm-1 at 623 K and higher in the order of TiILP≥ZrILP>SnILP. The activation energies, as expected, became lower in the order of ZrILPSnILP in bulk conductivities were not correlated with that of the activation energies probably because of the impureness of the ZrILP sample.

Abstract: Shell-core type TiP2O7-based electrolytes were synthesized by a low-temperature sol-gel method, and their conductivities were investigated by ac-impedance spectroscopy. The samples heat-treated at 500°C showed higher proton conductivities of 3.8 × 10-2 - 1 × 10-2 Scm-1 at intermediate temperatures (100 - 300°C). The conductivity decreased by reheat-treatments at 600°C and 700°C due to a decrease in the amount of the conductive amorphous shells. However, the mechanical strength of the sample pellet significantly increased by the reheat-treatment. The sample reheat-treated at 600°C kept high conductivities of 8.8 × 10-3 - 1 × 10-3 Scm-1 in a range of 100°C - 300°C.

Abstract: In order to reproduce the observed ionic conductivities and activation energies computationally, the potential parameters (PMs) were optimized for classical molecular dynamic simulations on Li ion conduction in the A-site deficient perovskite solid solution La056Li0.33TiO3 with disordered A-site ion arrangement. By the use of the optimized PMs, the conductivities and the activation energies were improved considerably from 4.1×10-3 Scm-1 to 4.4×10-2 Scm-1 at 800 K and 0.02 eV to 0.2 eV, respectively. The pair correlation functions calculated with the optimized PMs reveal that the Li-ions are located somewhat broadly mainly in the vicinity of the midpoint between the center of the A-site and the center of the bottleneck formed by four O2-, and that the simulated Li location is significantly related to the conductivity.

Abstract: Metallic ruthenium nano-particles supported on carbon were prepared from Ru3(CO)12 and highly-porous activated carbon by adsorption of the complex under boiling conditions in an acetone or cyclohexane solution, followed by H2 reduction at 200oC. Occupation of micropores with the precursor all through the carbon surface would diminish the BET surface area and the pore volume, whereas partial restoration of them by heating the material in H2 flow would be caused by complex decomposition and coagulative growth of Ru nano-particles (3.01 nm in average from TEM observation), which were surely lager in size than the pore diameter (2.15 nm determined by adsorption-isotherm measurements). Ru nano-particles were well dispersed on carbon.

Abstract: Lithium-ion conducting properties were investigated for a layered perovskite oxide Li2SrTa2O7 (LST) and defect-controlled LST, synthesized via solid state reactions. The ionic conductivities of A-site solid solutions Li2[Sr-(La2/3□1/3)-(La1/2Li1/2)]Ta2O7 (□ denotes vacancy.) suggested that lithium ions migrate in the Li-layer. The conductivity of Li-deficient (Li2-z□z)(LazSr1-z)Ta2O7 increased dramatically from 4.2 × 10-6 S cm-1 (z = 0, LST) to 1.6 × 10-3 S cm-1 (z = 0.2) at 400°C with increasing Li-vacancy concentration. This result obviously indicates that the conductivity of LST originate from the Li migration through vacancies in the Li-layer.

Abstract: Two types of oxide nanosheet-based materials, a H3O+-exchanged layered titanate and restacked titania nanosheets (H3O+-RE) were synthesized by soft chemical methods, and their oxygen reduction reaction (ORR) activities were examined by semi-steady-state voltammetry with a rotating ring-disc electrode at 70°C in 0.05 M H2SO4. Both samples showed similar onset potentials of the ORR, ~ 0.50 vs. reversible hydrogen electrode, while the efficiencies (Eff4) of the 4-electron reduction of oxygen depended on their nanostructures, i.e. the stacking morphology of nanosheets, specific surface area and kinds of cation between the nanosheets. Both H3O+-form samples showed high Eff4 values are compared with Cs+-form layered titanate.and the H+-form restacked titania nanosheets. This reveals that the H3O+ions and the number of the active sites for ORR are related to the ORR activity. The H3O+-RE exhibited the best Eff4 value (> 90%), which is comparable to that of a conventional 20 mass% Pt/C catalyst.

Abstract: Amorphous fine powder in the Li2O-Al2O3-TiO2-P2O5 (LATP) system were prepared directly from a mixture of Li2O, Al2O3, TiO2, and P2O5 as starting materials using a mechanical milling technique at room temperature. LATP glass-ceramics were obtained by heat treatment of the mechanochemically prepared amorphous powder over the crystallization temperature. X-ray diffraction peaks due to LiTi2(PO4)3 and AlPO4 crystals for LATP glass-ceramics were observed. Thus, high lithium ion conducting LATP glass-ceramics solid electrolytes were prepared successfully from the mechanochemically prepared amorphous powder. The LATP glass-ceramic fine particles were investigated as coating materials of LiCoO2 cathode in lithium ion batteries. The LATP glass-ceramics coated LiCoO2 electrode materials exhibited a good charge-discharge performance for charging up to a high voltage (4.5 V vs. Li/Li+).