Takashi Mouri

Preparation and properties of LiCoyMnxNi1−x−yO2 as a cathode for lithium ion batteries

Abstract The preparation of LiCoyMnxNi1−x−yO2 from LiOH·H2O, Ni(OH)2 and γ-MnOOH in air was studied in detail. Single-phase LiCoyMnxNi1−x−yO2 (0≦y≦0.3 and x=0.2) is obtained by heating at 830–900°C. The optimum heating temperatures are 850°C for y=0–0.1 and 900°C for y=0.2–0.3. Excess lithium (1≦z≦1.11 for y=0.2) and the Co doping level (0.05≦y≦0.2) do not significantly affect the discharge capacity of LizCoyMn0.2Ni0.8−yO2. The doping of Co into LiMn0.2Ni0.8O2 accelerates the oxidation of the transition metal ion, and suppresses partial cation mixing. Since the valence of the manganese ion in LiMn0.2Ni0.8O2 is determined to be 4, the formation of a solid solution between LiCoyNi1−yO2 and Li2MnO3 is confirmed.

Preparations of ZnO:Al transparent conducting films by d.c. magnetron sputtering

Abstract Highly conductive and transparent films of aluminium-doped ZnO (AZO) have been prepared by d.c. magnetron sputtering on a substrate placed parallel to the target. The spatial distributions of resistivity and thickness on the parallel substrate are controlled by plasma-controlled magnetron sputtering (PCMS) in an external d.c. magnetic field. AZO films with a resistivity as low as 2.7 × 10 −4 ohm cm can be produced on the substrate at temperatures above 250°C by the newly developed PCMS. The reduction in resistivity with increasing substrate temperature is related to the improvement in crystallinity of the AZO films. The carrier-scattering mechanism which dominates the mobility of the AZO films with the lowest resistivity is discussed from the experimental results and theoretical analysis.

Preparation of LiyMnxNi1-xO2 as a cathode for lithium-ion batteries

Abstract The preparation of LiyMnxNi1−xO2 from LiOH·H2O, Ni(OH)2 and γ-MnOOH under oxygen and flowing air is studied. Single phases of LiyMnxNi1−xO2 (0

Aluminium content dependence of milky transparent conducting ZnO:Al films with textured surface prepared by d.c. magnetron sputtering

Abstract Transparent and conductive milky zinc oxide (ZnO) films with a textured surface were prepared by d.c. magnetron sputtering using ZnO targets with an Al2O3 content in the range 0−2.0 wt.%. The grain growth and surface morphology were considerably dependent on the Al2O3 content, ranging from a disk-like textured surface for undoped ZnO films to a wedge-like textured surface for Al-doped (ZnO:Al) films prepared with a content above 0.5 wt.%. The resistivity of milky films post-annealed in an H2 atmosphere was independent of Al2O3 content from 0.75 to 2.0 wt.%, whereas it was reduced by a factor of 100 with Al impurity doping. The transmittance in the near-IR range of milky ZnO:Al films prepared with an Al2O3 content of 0.75 wt.% was considerably better than that of films prepared with a content of 2.0 wt.%. For solar cell applications of these films it was found that the optimal Al2O3 content of the ZnO target is about 0.75 wt.%. A sheet resistance as low as 2 ω□−1, a transmittance of 78% and a haze ratio of 65% at a wavelength of 550 nm were obtained for milky ZnO:Al films 3 μm thick prepared with an Al2O3 content of 0.75 wt.%.

Highly conductive and transparent ZnO:Al thin films prepared on high-temperature substrates by d.c. magnetron sputtering

Highly conductive and transparent aluminium-doped ZnO (AZO) thin films have been prepared on high-temperature substrates using d.c. magnetron sputtering. In AZO films, the spatial distribution of resistivity across substrates placed parallel to the target was improved by deposition at substrate temperatures above 300 °C. AZO films with resistivities of 2−5 x 10−4 Ω cm were prepared under sputter gas pressures of between 0.6 and 3.0 Pa and at a substrate temperature of 350 °C. In addition, milky AZO films with a textured surface were prepared on high-temperature substrates under sputtering conditions which suppressed the c-axis orientation. A total transmittance of 72% and a haze factor of 63% at a wavelength of 500 nm and a sheet resistance as low as 2.0 Ω sq−1 were obtained in milky AZO films 3 μm thick prepared at a sputter gas pressure of 12 Pa and a substrate temperature of 350 °C.

Large-Area Milky Transparent Conducting Al-Doped ZnO Films Prepared by Magnetron Sputtering

Large-area milky transparent conducting Al-doped ZnO (AZO) films with a wedgelike textured surface have been prepared by dc magnetron sputtering. Total transmittances of 84 and 77% and haze ratios of 10 and 53% at a wavelength of 550 nm were obtained in 1.2-µm- and 3-µm-thick milky AZO films, respectively: films were prepared at a substrate temperature of 350°C and a sputter argon gas pressure of 12 Pa. A resistivity of 5.5×10-4 Ωcm and a sheet resistance of 1.8 Ω/sq were obtained in a large-area 3-µm-thick AZO film postannealed at 300°C for 30 min in a hydrogen atmosphere.

Capacity failure on cycling or storage of lithium-ion batteries with Li–Mn–O ternary phases having spinel-framework structure and its possible solution

Instability of Li–Mn–O ternary phases having a spinel-framework structure especially at temperatures above 50°C is a problem in designing lithium-ion batteries with these materials. This paper describes the solubility of manganese ions from these materials in 1 M LiPF6EC/DMC (2/1 by volume), X-ray diffraction (XRD) analysis of these materials after solubility tests, and cycle tests of lithium cells with these materials at room temperature or at temperature higher than 50°C. Severe damage was observed in both solubility and cycle tests when Li–Mn–O ternary phases were operated or stored at temperatures higher than 50°C. The XRD examinations indicated that the spinel-framework structure changed in its line shape and location. In order to cope with this problem, we intensively examined the addition of transition metal elements into Li–Mn–O phases and found possible solution on this problem. One of the possible materials is Li[Cr0.1Mn1.9]O4 (Fd3m) which shows excellent performance on cycling and storage at 50°C.

Synthesis and electrochemical characteristics of Li(Ni · M)O2 (M = Co, Mn) cathode for rechargeable lithium batteries

Abstract The synthesis and electrochemical characteristics of LiNiO 2 and Li(Ni · M)O 2 (M = Co or Mn) as the cathode materials for rechargeable lithium batteries were investigated. It was clarified from these investigations that LiNiO 2 has been produced from crystalline NiO, which was derived from Ni(OH) 2 and LiOH, and that the property of NiO had some influence on the LiNiO 2 preparation. It was assumed that the formation of the layered structure has been inhibited by the existence of the Ni vacancy and Ni 3+ ion in NiO. The synthesis of a solid solution of Li(Ni · Co)O 2 suggested that a part of the Ni replacement by Co might inhibit the formation of the Ni vacancy of NiO and promote the formation of the layered structure. The capacity fading with increase in cycle number was suppressed by the replacement of a part of Ni with Co. We considered that the capacity fading was suppressed by the development of the layered structure wherein formation of Ni vacancy was suppressed by replacement with Co. LiNi 0.8 Co 0.2 O 2 prepared under the stream of oxygen gas showed a small irreversible capacity at first cycle and higher cycling capacity of ∼ 180 mA h g −1 .