Izumi Taniguchi

Particle morphology and electrochemical performances of spinel LiMn2O4 powders synthesized using ultrasonic spray pyrolysis method

Abstract Spinel lithium manganese oxide LiMn 2 O 4 powders with submicron, narrow-size-distribution, and phase-pure particles were synthesized by ultrasonic spray pyrolysis method from an aqueous lithium nitrate and manganese acetate solution. A tubular furnace with six independently controlled heating zones was used in this synthesis. The effect of axial temperature profile in the aerosol flow reactor on the particle properties of as-prepared LiMn 2 O 4 powders was examined with X-ray diffraction (XRD), the Brunauer–Emmett–Teller (BET) method, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Spinel LiMn 2 O 4 powders were successfully synthesized at both constant temperature distribution (1073 K) and increasing one (473-473-673-873-1073-1073 K) in the reactor at various gas flow rates ranging from 0.5 to 4.0 dm 3 /min. The as-prepared samples were used as cathode active materials for lithium-ion battery and their charge/discharge properties have been investigated. Their electrochemical properties in terms of cycle performance were also discussed.

LiMg x Mn1 − x PO4 / C Cathodes for Lithium Batteries Prepared by a Combination of Spray Pyrolysis with Wet Ballmilling

The LiMg x Mn 1-x PO 4 /C (x = 0, 0.02, 0.04, 0.12) composite cathode was successfully prepared by a combination of spray pyrolysis and wet ballmilling with heat-treatment. The composite cathode had narrow particle size distribution with an average particle size of 99 nm. The Mg doping on the Mn site led to the electrochemical performance enhancement of the composite cathode, which was confirmed by cyclic voltammetry, ac impedance spectroscopy, and charge-discharge tests. The Mg-doped composite cathode exhibited a high discharge capacity in lithium cell, which remarkably increased with an increase in the charge cutoff voltage under galvanostatic charge-discharge. The LiMg 0.04 Mn 0.96 PO 4 /C cathode exhibited a discharge capacity of 154 mAh g -1 (above 93% of the theoretical value) at 0.1C when charge-discharged galvanostatically to 4.9 V. Along with enhanced discharge capacity, the cell exhibited a good rate capability under the galvanostatic charge-discharge. Under the trickle mode conditions, the cell exhibited discharge capacities of 154, 136, 106, and 74 mAh g -1 at 0.05, 0.1, 1, and 5C, respectively.

Fabrication of La1−xSrxCo1−yFeyO3 thin films by electrostatic spray deposition

Abstract The deposition of La 1− x Sr x Co 1− y Fe y O 3 (0≦ x ≦0.4 and 0≦ y ≦1) thin films on a stainless steel or gadolinium-doped ceria substrate was studied using the electrostatic spray deposition (EDS) technique. The precursor solution was prepared by dissolving the correct amount of lanthanum nitrate, strontium chloride, cobalt nitrate and iron nitrate into a mixture of 33 vol.% ethanol and 67 vol.% butyl carbitol. The effect of the process parameters, such as deposition temperature, deposition time and liquid flow rate, on the surface morphology and microstructure of the thin films were examined with scanning electron microscopy (SEM). The deposited La 1− x Sr x Co 1− y Fe y O 3 thin films were amorphous or nanocrystalline at the used deposition temperature (573 K). Subsequently, the samples were heated at 1173 K for 2 h and were studied using X-ray diffraction (XRD). As a result, the crystal structure of the samples transformed to the desired perovskite phase. The chemical analysis of the thin films was studied by energy dispersion X-ray (EDX) analysis. The observed chemical compositions of the samples were in fair agreement with the ones of the starting precursor solutions.

Electrostatic spray deposition of Gd0.1Ce0.9O1.95 and La0.9Sr0.1Ga0.8Mg0.2O2.87 thin films

Abstract The deposition of gadolinia-doped ceria (CGO, Gd 0.1 Ce 0.9 O 1.95 ) and LaGaO 3 -based perovskite oxides (LSGM, La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 2.87 ) thin films on a stainless steel substrate was studied using the electrostatic spray deposition (EDS) technique. The effect of process conditions, such as deposition temperature, deposition time and liquid flow rate, on the surface morphology and microstructure of thin films was examined with scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The deposited CGO films with a highly porous and three-dimensional interconnected structure were obtained at a liquid flow rate of 0.5 ml/h, a deposition temperature of 503 K and a deposition time ranging from 0.5 to 1 h. On the other hand, the deposited LSGM thin films with porous microstructure were also obtained at the deposition time of 1 h, the deposition temperature of 533 K and the liquid flow rate of 0.5 ml/h. The deposited CGO and LSGM thin films were amorphous at the used deposition temperature. Subsequently, the samples were annealed at 1173 K for 2 h and the desired crystal structures were obtained. The chemical analysis of the thin films was investigated by energy dispersive X-ray (EDX) analysis. The observed chemical compositions of the samples were in a fair agreement with those of the starting solutions.

Electrochemical properties of stoichiometric CuS coated on carbon fiber paper and Cu foil current collectors as cathode material for lithium batteries

We prepared stoichiometric CuS by spray pyrolysis at 400 °C, followed by low temperature heat treatment at 150 °C for 1 h to conduct electrochemical reaction mechanism studies. The cathode electrode coated on carbon fiber paper (CFP) and Cu foil current collectors were analyzed by ex situ XRD after cycling at 0.02C and 1.2–3.0 V with Li/Li+. Stoichiometric CuS coated on a CFP current collector suffered from the 1st cycle irreversibility and rapid capacity fading after the 5th cycle to 120 mA h g−1, owing to the formation of a low crystallinity CuS after the 1st charge, and the dissolution of lithium polysulfides (Li2Sx, 2 < x ≤ 8) in the electrolyte. On the other hand, stoichiometric CuS coated on a Cu foil current collector showed improved capacity of 460 mA h g−1 after the 5th cycle. The excess Cu cations on the Cu foil introduced to CuxS led to the formation of Cu1.96S instead of CuS in the fully charged state, which enhanced the capacity retention and the efficient Li2Sx utilization. However, the gradual Li2Sx dissolution in the electrolyte and migration to the lithium metal side after 15 cycles at 0.1C still caused cell deterioration. To trap Li2Sx, we inserted a CFP interlayer between the stoichiometric CuS electrode coated on a Cu foil current collector and separator. The modified cell showed a stable capacity of 440 mA h g−1 for 200 cycles at 1C and excellent rate capability with a capacity of 340 mA h g−1 at 10C.

LiMnPO 4 Olivine as a Cathode for Lithium Batteries

The olivine structured mixed lithium-transition metal phosphates LiMPO4 (M = Fe, Mn, Co) have attracted tremendous attention of many research teams worldwide as a promising cathode materials for lithium batteries. Among them, lithium manganese phosphate LiMnPO4 is the most promising considering its high theoretical capacity and operating voltage, low cost and environmental safety. Various techniques were applied to prepare this perspective cathode for lithium batteries. The solution based synthetic routes such as spray pyrolysis, precipitation, sol-gel, hydrothermal and polyol synthesis allow preparing nanostructured powders of LiMnPO4 with enhanced electrochemical properties, which is mostly attributed to the higher chemical homogeneity and narrow particle size distribution of the material. Up-to-date, the LiMnPO4/C composites prepared by the spray pyrolysis route have the best electrochemical performance among the reported in the literature.

SYNTHESIS OF NANOSTRUCTURED LiM0.15Mn1.85O4 (M = Mn, Co, Al, AND Fe) PARTICLES BY SPRAY PYROLYSIS IN A FLUIDIZED BED REACTOR

A novel technique has been developed to directly produce fine ceramic powders from liquid solution via spray pyrolysis in a fluidized bed reactor (SPFBR). Using this technique the preparation of LiM0.15Mn1.85O4 (M = Mn, Co, Al, and Fe), which are the most promising cathode materials for lithium-ion batteries, has been carried out at a superficial velocity U0 of 0.71 m/s, a reactor temperature T of 800°C, and a static bed height Ls of 100 mm. The as-prepared powders were spherical nanostructured particles that comprised primary particles of a few tens of nanometers in size, and they exhibited a pure cubic spinel structure without any impurities in the XRD patterns. The chemical composition of as-prepared samples showed good agreement with the theoretical values that proved stoichiometric formulae of the compounds. The specific surface area of as-prepared LiM0.15Mn1.85O4 (M = Mn, Co, Al, and Fe) powders decreases with increasing the static bed height in each doping metal, while the crystallite size increases with the static bed height. As a result, the as-prepared powders showed larger crystallite size and smaller specific surface area than those prepared by conventional spray pyrolysis.

ABSORPTION OF CARBON DIOXIDE WITH A FREELY FALLING AQUEOUS SODIUM HYDROXIDE SOLUTION DROP

Measurements for the rates of absorption of carbon dioxide from carbon dioxide-air mixtures with a water and an aqueous sodium hydroxide solution drop falling freely were made for Fourier number Fo = 1.53 · 10-5 — 9.83 × 10-5, initial concentration of aqueous sodium hydroxide solution CBO — 0.05 — 0,4 mol/1 and feed gas concentration of carbon dioxide y = 0.05 — 1.0. Observed dimensionless rates of absorption were compared with the theoretical values by the present model and gave a good agreement with theory. The effect of drop diameter on the enhancement factor, which is a measure of the effect of chemical reaction on the rates of absorption of carbon dioxide with a freely falling alkaline solution drop, were also discussed by using numerical simulation