Koichi Kubo

Synthesis and electrochemical properties for LiNiO2 substituted by other elements

Abstract Li 1 − x Ni 1 − x O 2 − y F y as the cathode materials for rechargeable lithium batteries were synthesized by co-substitution of nickel sites and oxygen sites for LiNiO 2 . The materials were found to possess good properties on charge/discharge cycling without significant deterioration of the initial capacity. In order to investigate the reason the cycle properties were improved, we performed experiments focusing on the crystallographic point of view using X-ray diffractometry accompanied by electrochemical property. These materials were found to restrain none of crystallographic change during charge/discharge regardless of the amount of substitution. According to the charge/discharge curve, the materials indicate relatively low internal impedance. Thus, the main reason for the improvements of the cycle properties may be caused by mechanism which has no direct relation to the above crystallographic change.

Synthesis and charge–discharge properties of Li1+xNi1−x−yCoyO2−zFz

LiNiO 2 is one of the best cathode active materials for applying to lithium rechargeable batteries because of large capacity. However, its unsatisfactory cycling properties and difficulties in handling are not yet to be improved. It was found by some groups [M.G.S.R. Thomas, W.I.F. David, J.B. Goodenough, P. Groves, Mater. Res. Bull. 20 (1985) 1137; J.R. Dahn, U. von Sacken, C.A. Michal, Solid State Ionics 44 (1990) 87] that cation substitution reduces the lattice deformation during charging or discharging and improves the cycling properties. On the other hand, we reported [T. Ohzuku, A. Ueda, M. Kouguchi, J. Electrochem. Soc. 12 (1995) 4033] that addition of LiF to the starting materials, causing fluorine substitution for the anion, is also effective to obtain a better cycling life for LiNiO 2 , though the problem of the lattice deformation is not alleviated. Thus, it was expected that simultaneous substitution of cation- and anion sites might be useful. We synthesized Li 1+x Ni 1-x-y Co y O 2-z F z by an ordinary solid state reaction and evaluated the charge-discharge properties of this series of samples. The initial discharge capacity of Li 1.075 Ni 0.755 Co 0.17 O 1.9 F 0.1 was 182 mAh/g.The capacity decrease rate was only 2.8% in the first 100 cycles, and became even smaller as the cycle number increased. The result suggests that each of the Co- and F substitution independently contributes to the improvement of cycling properties of LiNiO 2 .

Development of blade for floating type current turbine system

The KUROSHIO is one of the ocean currents flowing stably near the coast of Japan throughout the year, and power generation technology using this ocean current energy is now attracting attention in Japan due to its potential as a clean and stable energy source. Slow current velocity and deep water depth are technical challenges of the current turbine system in the KUROSHIO Current. The authors have been engaged in the research and development of a floating type current turbine system moored on the seabed and floating on the sea. This system consists of large twin-turbines and simple mooring for deep-sea deployment as shown in Fig. 1, and it is expected to operate with a high capacity factor. This paper discussed about the turbine output characteristics by turbine blades which were confirmed through CFD (Computational Fluid Dynamics) analysis, towing tank test and the impact of turbine blade deformation which was measured by towing tank test, obliquely inflow and cross-beam.

Numerical simulation of turbulence flow in a Bulb turbine

In this paper, high accuracy performance prediction method based on entire flow passage for a Bulb turbine is presented. The performance is predicted by solving steady and unsteady Reynolds-Averaged Navier-Stokes equations, Large Eddy simulation and Detached Eddy Simulation. The prediction accuracy was evaluated to compare with the model test results for efficiency characteristic, pressure fluctuation characteristic and velocity distribution at runner inlet and outlet of NQE 0.8 Bulb model turbine. As for the efficiency near the on-cam condition, it is possible to determine with high accuracy in the steady RANS analysis. However, for the analysis accuracy regarding pressure fluctuation characteristic and turbine characteristics at off-cam operating condition, it found that there is a need to further study. Evaluated prediction method for the turbine flow and performance is introduced to facilitate the future design and research works on Bulb type turbine.