Yoshio Ukyo

Memory effect in a lithium-ion battery

Memory effects are well known to users of nickel-cadmium and nickel-metal-hydride batteries. If these batteries are recharged repeatedly after being only partially discharged, they gradually lose usable capacity owing to a reduced working voltage. Lithium-ion batteries, in contrast, are considered to have no memory effect. Here we report a memory effect in LiFePO4-one of the materials used for the positive electrode in Li-ion batteries-that appears already after only one cycle of partial charge and discharge. We characterize this memory effect of LiFePO4 and explain its connection to the particle-by-particle charge/discharge model. This effect is important for most battery uses, as the slight voltage change it causes can lead to substantial miscalculations in estimating the state of charge of batteries.

Capacity-Fading Mechanisms of LiNiO2-Based Lithium-Ion Batteries II. Diagnostic Analysis by Electron Microscopy and Spectroscopy

We used a suite of transmission electron microscopy (TEM) and associated electron spectroscopy methods to examine the local structure and changes in the electronic structure of LiNi 0.8 Co 0.15 Al 0.05 O 2 positive electrode material. We found a scattered rock-salt phase near grain surfaces and grain boundaries, where Ni 3+ turned to Ni 2+ , deduced from relative intensity ratios and fine structures of the L 2,3 white-line peaks of the transition metals. The spatial distribution of the degraded phase throughout the secondary particle was found using a scanning TEM-electron energy loss spectroscopy spectral imaging technique and multivariate analysis. The degradation process and its relationship to the surface reactions with electrolytes is discussed based on the spatial-distribution map of the degraded phases.

Capacity-Fading Mechanisms of LiNiO2-Based Lithium-Ion Batteries I. Analysis by Electrochemical and Spectroscopic Examination

I. Analysis by Electrochemical and Spectroscopic Examination Tsuyoshi Sasaki,* Takamasa Nonaka, Hideaki Oka, Chikaaki Okuda, Yuichi Itou, Yasuhito Kondo, Yoji Takeuchi, Yoshio Ukyo,* Kazuyoshi Tatsumi, and Shunsuke Muto* Toyota Central Research and Development Laboratories, Incorporated, Nagoakute 480-1192, Japan Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan

Study on current efficiency of steam electrolysis using a partial protonic conductor SrZr0.9Yb0.1O3−α

Abstract The current efficiency of steam electrolysis was measured in the temperature range from 460 to 600°C using a steam electrolysis cell constructed with a partial protonic conductor SrZr 0.9 Yb 0.1 O 3− α as an electrolyte and Pt cermet electrodes. The efficiency was increased with increasing partial pressure of water vapor and temperature. The results were considered in relation to the reaction rates at the anode and cathode. Under the operating conditions of steam electrolysis, the reaction rate of producing H 2 from protons at the cathode was found to be faster than that of oxidizing water vapor into protons and O 2 at the anode. Therefore, the average concentration of protons in the partial protonic conductor during electrolysis decreased. On the other hand, the average concentration of holes increased. This is considered to decrease the efficiency of steam electrolysis. It was found that the effective transport numbers of charge carriers in the partial protonic conductor were controlled by the reaction rates at the electrodes at relatively low temperatures at which the equilibria between the atmosphere and defects in the partial protonic conductor were difficult to obtain.

Real-time observations of lithium battery reactions—operando neutron diffraction analysis during practical operation

Among the energy storage devices for applications in electric vehicles and stationary uses, lithium batteries typically deliver high performance. However, there is still a missing link between the engineering developments for large-scale batteries and the fundamental science of each battery component. Elucidating reaction mechanisms under practical operation is crucial for future battery technology. Here, we report an operando diffraction technique that uses high-intensity neutrons to detect reactions in non-equilibrium states driven by high-current operation in commercial 18650 cells. The experimental system comprising a time-of-flight diffractometer with automated Rietveld analysis was developed to collect and analyse diffraction data produced by sequential charge and discharge processes. Furthermore, observations under high current drain revealed inhomogeneous reactions, a structural relaxation after discharge, and a shift in the lithium concentration ranges with cycling in the electrode matrix. The technique provides valuable information required for the development of advanced batteries.

Surface-Sensitive X-Ray Absorption Study on LiNi0.8Co0.15Al0.05O2 Cathode Material for Lithium-Ion Batteries

We have used Ni and Co K-edge conversion electron yield X-ray absorption fine structure (CEY-XAFS) and conventional XAFS in transmission mode to investigate LiNi 0.8 Co 0.15 Al 0.05 O 2 , one of the promising cathode materials for Li-ion batteries. The former technique is surface-sensitive, having a probing depth of -90 nm, while the latter is bulk-sensitive. X-ray absorption near edge structure analysis revealed that the bulk-averaged Ni valences for cycle-tested cells and aging-tested cells are lower than that for a fresh cell throughout charging. Further reduction of Ni atoms is observed at the surface of the cathode material particles, and the ranges of the Ni valence change upon charging are narrower than that for a fresh cell, indicating the presence of Ni atoms which are unaffected by charging. Extended X-ray absorption fine structure analysis revealed that the change in bond lengths [Ni-O, Ni-M (M = Ni,Co), Co-0, and Co-M] is consistent with the change in the Ni valence. These electronic and structural changes occur predominantly at the surface and are probably the main causes of capacity fading.

Reduction of nitrogen oxide by steam electrolysis cell using a protonic conductor SrZr0.9Yb0.1O3−α and the catalyst Sr/Al2O3

Abstract A steam electrolysis cell was constructed with a high-temperature type protonic conductor, SrZr0.9Yb0.1O3−α. The reduction of nitrogen oxide (NO) by hydrogen, which was produced by a steam electrolysis cell, was examined. Helium gas with 8% O2 and 1000 ppm NO was used as a model gas for the exhaust gas from automotive engines operating under lean-burn condition. The removal efficiency of NO was measured, using steam electrolysis cells with different catalysts on the cathodes. A mixture of Pt-sponge and Sr/Al2O3 catalyst was found to be most effective for the preferred reduction of NO in the presence of excess O2. It was suggested that the preferred reduction of NO occurred via the electrochemical reduction of NO absorbed into Sr/Al2O3, not via the chemical reduction of NO by H2 gas.

Atomic-Scale Observations of (010) LiFePO4 Surfaces Before and After Chemical Delithiation

The ability to view directly the surface structures of battery materials with atomic resolution promises to dramatically improve our understanding of lithium (de)intercalation and related processes. Here we report the use of state-of-the-art scanning transmission electron microscopy techniques to probe the (010) surface of commercially important material LiFePO4 and compare the results with theoretical models. The surface structure is noticeably different depending on whether Li ions are present in the topmost surface layer or not. Li ions are also found to migrate back to surface regions from within the crystal relatively quickly after partial delithiation, demonstrating the facile nature of Li transport in the [010] direction. The results are consistent with phase transformation models involving metastable phase formation and relaxation, providing atomic-level insights into these fundamental processes.

The effect of a small amount of impurity on the oxidation of Si3N4 ceramics

To investigate the effect of a small amount of impurity, especially Ca(CaO), on the oxidation of Si3N4 ceramics at high temperatures, two kinds of Si3N4 ceramics with different amounts of impurities were fabricated. The decrease in the strength of Si3N4 ceramics containing calcium as an impurity became severe when oxidation time was longer and temperature was higher. The decrease in the strength was caused by the formation of pits. It is estimated that pits are formed due to the high concentration of calcium in the oxidized layer near to the pits.

Performance of electrolysis cells with proton and oxide-ion conducting electrolyte for reducing nitrogen oxide

Abstract A steam electrolysis cell was constructed with a proton conductor SrZr 0.9 Yb 0.1 O 3− α as an electrolyte. The steam electrolysis cell efficiently reduced nitrogen oxide (NO) on the cathode, using hydrogen produced by steam electrolysis as a reducing agent at around 460 °C. When a Pt/Ba/Al 2 O 3 catalyst was placed on the cathode, NO was reduced even under an O 2 -rich atmosphere. An electrolysis cell was also constructed with an oxide-ion conductor 8 Y–ZrO 2 as an electrolyte. The cell could reduce NO on the cathode, not only electrochemically electrolyzing NO directly but also chemically using hydrogen produced by steam electrolysis. However, the cell with the oxide-ion conductor could not reduce NO in an atmosphere containing O 2 .