フォード自動車における労働条件引き下げの実態とその影響 : 2009年におこなわれた労働協約の改訂を中心にして

departmental bulletin pape

Observation of the Color-Suppressed Decay B̅ 0→D0π0

journal articl

Microwave-Assisted Solvothermal Synthesis of Spinel AV₂O₄ (M = Mg, Mn, Fe, and Co)

Lower-valent vanadium oxide spinels AV₂O₄ (A = Mg, Mn, Fe, and Co) consisting of A²⁺ and V³⁺ ions have been synthesized by a low-temperature microwave-assisted solvothermal (MW-ST) synthesis process in a tetraethylene glycol (TEG) medium. The oxides are formed within a short reaction time of 30 min at 300 °C. Subsequent postheat treatment of the oxides at elevated temperatures in inert or reducing atmospheres results in an instability of the spinel phase, especially CoV₂O₄ due to the ease of formation of metallic Co, demonstrating the advantage of the low-temperature MW-ST process in accessing these oxides. This MW-ST synthesis approach is attractive for synthesizing other lower-valent transition-metal oxides that are otherwise difficult to obtain by conventional synthesis methods and for subsequent study of their unique physical and chemical properties

Crystal-Chemical Guide for Understanding Redox Energy Variations of M^2+/3+ Couples in Polyanion Cathodes for Lithium-Ion Batteries

A crystal-chemical guide is provided for understanding how factors such as the crystal structure and covalency of the polyanion affect the M^2+/3+ redox energies in polyanion cathodes. Although there are more rigorous techniques available, our approach is precise in spite of being simple. We show that an accurate prediction can be made with regard to the voltages delivered based on a basic understanding of how the coordination of the transition-metal ion affects the covalency of the M-O bond. Additionally, a new method for assessing the covalency of the polyanion (beyond the electronegativity of the countercation) is presented and used to explain why the voltage delivered by Li₂MP₂O₇ cathodes is higher than that of LiMPO₄. Furthermore, a comparison of the silicate and phosphate structures reveals that edge sharing between transition metal polyhedra and other cation polyhedra has an opposite effect on the voltage delivered by these materials. For instance, edge sharing with LiO₄ polyhedra in the silicates raises the M^2+/3+ redox energy, whereas edge sharing with PO₄ polyhedra in the phosphates lowers the M^2+/3+ redox energy. This is due to a difference in the strength of the repulsive force exerted on the transition metal by the P⁵⁺ cation when compared to Li⁺. This observation is significant since edge sharing has generally been viewed as a structural feature that lowers the redox energy. Lastly, crystal field splitting consideration alone is not sufficient to understand the voltage trends for polyanion cathodes and one must consider the contributions of the structure and/or the inductive effect. Our analysis provides new insights that may prove useful in tuning the voltage of existing polyanion systems and in the design of new cathode materials

Microwave-Assisted Synthesis of NaCoPO₄ Red-Phase and Initial Characterization as High Voltage Cathode for Sodium-Ion Batteries

Transition metal-containing polyanion compounds are attractive for use as cathode materials in sodium-ion batteries (SIB) because they possess elevated higher intrinsic electrochemical potentials versus oxide analogs given the same M^{<i>n</i>+/(<i>n</i>+1)+} redox couple, which leads to higher energy densities. NaMPO₄ (M = transition metal) compounds have a driving force to form into the electrochemically inactive maricite phase when using conventional methods. Herein we report on the synthesis of a NaCoPO₄ (NCP) polymorph (“Red”-phase) by a microwave-assisted solvothermal process at 200 °C using tetraethylene glycol as the solvent. Ex situ XRD, XANES, and electrochemical data are used to determine the reversibility of the Co^2+/3+ redox center

Direct Monte-Carlo Simulation on Rarefied Gas Flow

application/pdfThe direct simulation Monte-Carlo method has been used to study the behaviour of the rarefied gas flow through the two-dimensional slit, where the pressure ratio between the upstream and the downstream of the slit is high enough to neglect the downstream pressure. In order to correct the error due to the finiteness of the simulated physical-space, the equilibrium velocity distribution modified by the addition of the stream velocity normal to the boundary surface, instead of the equilibrium one, is assumed to the molecules which flow into the simulated region through the upstream boundary. About 16,000 molecules of the hard sphere model and 800 cells are used in the calculation. The conductance of the slits calculated by the simulation is in good agreement with the experimental result.departmental bulletin pape

High-Capacity, Aliovalently Doped Olivine LiMn_{1–3<i>x</i>/2}V_<i>x</i>□_<i>x</i>/2PO₄ Cathodes without Carbon Coating

A substantial amount of Mn²⁺ has been aliovalently substituted by V³⁺ in cation-deficient LiMn_{1–3<i>x</i>/2}V_<i>x</i>□_<i>x</i>/2PO₄ (0 ≤ <i>x</i> ≤ 0.20) by a low-temperature (<300 °C) microwave-assisted solvothermal (MW-ST) process. The necessity of a low-temperature synthesis to achieve higher levels of doping is demonstrated as the solubility of vanadium decreases with the formation of impurity phases on heating the samples to ≥575 °C. Soft X-ray absorption spectroscopy reveals enhanced Mn–O hybridization in the vanadium-doped samples, which is believed to facilitate an increase in capacity with increasing vanadium content in the lattice. For example, a high capacity of 155 mAh/g is achieved above a cutoff voltage of 3 V without any carbon coating for the <i>x</i> = 0.2 sample. The vanadium substitution enhances the overall kinetics of the material by lowering the charge-transfer impedance and increasing the lithium-diffusion coefficient

Revealing Grain-Boundary-Induced Degradation Mechanisms in Li-Rich Cathode Materials

Despite their high energy densities, Li- and Mn-rich, layered–layered, xLi2MnO3·(1 – x)­LiTMO2 (TM = Ni, Mn, Co) (LMR-NMC) cathodes require further development in order to overcome issues related to bulk and surface instabilities such as Mn dissolution, impedance rise, and voltage fade. One promising strategy to modify LMR-NMC properties has been the incorporation of spinel-type, local domains to create “layered–layered–spinel” cathodes. However, precise control of local structure and composition, as well as subsequent characterization of such materials, is challenging and elucidating structure–property relationships is not trivial. Therefore, detailed studies of atomic structures within these materials are still critical to their development. Herein, aberration corrected-scanning transmission electron microscopy (AC-STEM) is utilized to study atomic structures, prior to and subsequent to electrochemical cycling, of LMR-NMC materials having integrated spinel-type components. The results demonstrate that strained grain boundaries with various atomic configurations, including spinel-type structures, can exist. These high energy boundaries appear to induce cracking and promote dissolution of Mn by increasing the contact surface area to electrolyte as well as migration of Ni during cycling, thereby accelerating performance degradation. These results present insights into the important role that local structures can play in the macroscopic degradation of the cathode structures and reiterate the complexity of how synthesis and composition affect structure–electrochemical property relationships of advanced cathode designs

Unveiling Morphology and Crystallinity Dynamics in Ni_<i>x</i>Mn_1–<i>x</i>CO₃ Cathode Precursors through Batch-Mode Coprecipitation

This study delves into the synthesis and control of NixMn1–xCO3, a critical class of Mn-rich, Co-free precursors vital for cathode-oxide materials in energy storage and conversion technologies. Employing batch-mode coprecipitation, we systematically generated samples with varying Ni concentrations (x = 0, 0.1, 0.3, 0.5, 0.7, and 0.9) and conducted a comprehensive analysis of their compositions, crystallinities, transition-metal distributions, and particle morphologies through both experimental and computational methods. A significant variation in particle size and crystallinity was observed, contingent on the Ni content. A pivotal transition emerged at Ni concentrations above x = ∼0.5, transforming uniform morphologies, such as spherical, monodisperse, pseudo-single-crystalline particles, into bimodal, polycrystalline structures. Furthermore, the study highlights the role of Ni–ammonia complexes leading to Ni-deficient precipitates and underscores the importance of ammonia concentration in achieving precise Ni content control. This study unveils critical reaction conditions governing Mn-rich precursor properties that are vital for cathode-oxides, emphasizing the need for meticulous synthetic control and offering the potential for practical applications in advanced energy storage and conversion systems

Redox Mechanisms and Migration Tendencies in Earth-Abundant 0.7Li₂MnO₃·0.3LiFeO₂ Cathodes: Coupling Spin-Resolved X‑ray Absorption Near Edge and X‑ray Absorption Fine Structure Spectroscopies

We report the use of iron 1s3p resonant X-ray emission processes to conduct spin-selective, high-energy resolution fluorescence detected X-ray absorption near-edge spectroscopy (HERFD-XANES) on an iron-containing, lithium- and manganese-rich, fully earth-abundant cathode material, Li1.3Mn0.5Fe0.2O2 (0.7Li2MnO3·0.3LiFeO2). Coupling this technique with conventional Mn K-edge XANES and detailed extended X-ray absorption fine structure (EXAFS) analysis from both the Mn and Fe vantage points, we gain fundamental insights into the redox processes and migration tendencies of transition metals in this cathode material at the bulk level. We show that during the first charge, Fe3+ undergoes oxidation to form Fe4+ prior to the activation plateau. Toward the end of activation, a significant fraction of the iron is present as tetrahedral Fe3+. This observation reveals that iron migration from octahedral to tetrahedral sites and iron reduction are initiated during activation. Upon first discharge from the activated state, a continuous and overlapping reduction of both Fe and Mn is observed, with Fe largely restored back as an octahedrally coordinated Fe3+. The manganese local environment gradually changes to a distorted cooperative Jahn–Teller Mn3+ structure during discharge, with the clear presence of two Mn–O as well as two Mn–Mn correlation distances at 2.0 V. The significant reduction of manganese in the very first discharge is distinctly different from that seen in typical nickel-based lithium-manganese-rich materials but is similar to that observed for pure Li2MnO3. These findings shed light on key structure–property correlations in the cathode material and point to a causative relationship between the redox mechanisms as well as structural changes endured by the material and relatively poor performance during extended electrochemical cycling