Masao Yonemura

Float charging at 4.2 V with periodical discharging leads to degradation of lithium-ion batteries, mainly caused by resistance increase in the positive electrode (RIPE). Restricting the charging voltage to 4.0 V alleviates the degradation.

K₂NiF₄‐type Ba–Li oxyhydride (BLHO) transitions to a so‐called hydride superionic conductor, exhibiting a high and essentially temperature‐independent hydride ion (H⁻) conductivity over 0.01 S cm⁻¹ through the disordering of H⁻ vacancies above 300 °C. In this study, a Ba–Li–Na–H–O oxyhydride system synthesized in which lithium is partially substituted with sodium in BLHO and investigated the effects of Na content on the phase transition behavior and the conductivity. Structural refinements and differential scanning calorimetry experiments confirmed a lowering trend in the phase transition temperatures and decreasing enthalpy changes for the transition with increasing Na content. Substitution of not − sites at room temperature and improved conductivities by more than two orders of magnitude in the low‐temperature region (T < 300 °C) before the phase transition. These findings clearly show that introducing Na into the lattice effectively stabilizes the high‐conductive phase of BLHO.

Ba_1.75LiH_2.7O_0.9 exhibits H⁻ conductivity over 10⁻² S cm⁻¹ above 315 °C due to phase transitions. In this work, a reduction of the phase transition temperature and an improvement of conductivity at lower temperatures by K/Ba substitution were confirmed.

A quantitative nondestructive Bragg-edge imaging technique for power-storage degradation was developed using commercial prismatic-shaped lithium-ion battery cells. The C or Li atoms/ions column density [cm⁻²] images for five phases of the negative electrode material (graphite, Li_0.04C₆, Li_0.2C₆, Li_0.5C₆, and Li_1.0C₆) with a 1 mm spatial resolution were obtained by considering the crystalline orientation for both fresh and fatigue cells. In the fresh cell, most of the graphite was uniformly converted to Li_1.0C₆ by charging, and in the fatigue cell, the graphite changed to various phases (especially, Li_1.0C₆ and Li_0.5C₆) by charging, and their spatial distributions were nonuniform.

Hydrogen transport in solids, applied in electrochemical devices such as fuel cells and electrolysis cells, is key to sustainable energy societies. Although using proton (H⁺) conductors is an attractive choice, practical conductivity at intermediate temperatures (200–400 °C), which would be ideal for most energy and chemical conversion applications, remains a challenge. Alternatively, hydride ions (H^–), that is, monovalent anions with high polarizability, can be considered a promising charge carrier that facilitates fast ionic conduction in solids. Here, we report a K₂NiF₄-type Ba–Li oxyhydride with an appreciable amount of hydrogen vacancies that presents long-range order at room temperature. Increasing the temperature results in the disappearance of the vacancy ordering, triggering a high and essentially temperature-independent H^– conductivity of more than 0.01 S cm^–1 above 315 °C. Such a remarkable H^– conducting nature at intermediate temperatures is anticipated to be important for energy and chemical conversion devices.

The development of an energy storage system with abundant elements is a key challenge for a sustainable society, and the interest of Na intercalation chemistry is extending throughout the research community. Herein, the impact of Ti integration into NaMnO ₂ in a binary system of x NaMnO ₂ –( 1 – x ) TiO ₂ ( 0.5 ≤ x ≤ 1 ) is systematically examined for rechargeable Na battery applications. Stoichiometric NaMnO ₂ , which is classified as an in-plane distorted O ′ 3-type layered structure, delivers a large initial discharge capacity of approximately 200 mAh g ^-1 , but insufficient capacity retention is observed, most probably associated with dissolution of Mn ions on electrochemical cycles. Ti-substituted samples show highly improved electrode performance as electrode materials. However, the appearance of a sodium-deficient phase, Na ₄ Mn ₄ Ti ₅ O ₁₈ with a tunnel-type structure, is observed for Ti-rich phases. Among the samples in this binary system, Na _0.8 Mn _0.8 Ti _0.2 O ₂ ( x = 0.8 ), which is a mixture of a partially Ti-substituted O ′ 3-type layered oxide (Na _0.88 Mn _0.88 Ti _0.12 O ₂ ) and tunnel-type Na ₄ Mn ₄ Ti ₅ O ₁₈ as a minor phase elucidated by Rietveld analysis on both neutron and X-ray diffraction patterns, shows good electrode performance on the basis of energy density and cyclability. Both phases are electrochemically active as evidenced by in situ X-ray diffraction study, and the improvement of reversibility originates from the suppression of Mn dissolution on electrochemical cycles. From these results, the feasibility of Mn-based electrode materials for high-energy rechargeable Na batteries made from only abundant elements is discussed in detail.

Thermoelectric material SnSe has aroused world-wide interests in the past years, and its inherent strong lattice anharmonicity is regarded as a crucial factor for its outstanding thermoelectric performance. However, the understanding of lattice anharmonicity in SnSe system remains inadequate, especially regarding how phonon dynamics are affected by this behavior. In this work, we present a comprehensive study of lattice dynamics on Na_0.003Sn_0.997Se_0.9S_0.1 by means of neutron total scattering, inelastic neutron scattering, Raman spectroscopy as well as frozen-phonon calculations. Lattice anharmonicity is evidenced by pair distribution function, inelastic neutron scattering and Raman measurements. By separating the effects of thermal expansion and multi-phonon scattering, we found that the latter is very significant in high-energy optical phonon modes. The strong temperature-dependence of these phonon modes indicate the anharmonicity in this system. Moreover, our data reveals that the linewidths of high-energy optical phonons become broadened with mild doping of sulfur. Our studies suggest that the thermoelectric performance of SnSe could be further enhanced by reducing the contributions of high-energy optical phonon modes to the lattice thermal conductivity via phonon engineering.

X‐ray total scattering measurements are carried out for the typical electrolyte used in lithium‐ion batteries, that is, the mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) electrolyte with LiPF₆ salt. The obtained pair distribution function is compared with that of the EC/EMC solvent without LiPF₆, to investigate the effect of the Li⁺ cation on the intramolecular structure. It is found that the peak shift corresponding to the shrinking of the CO bonds is induced by dissolving LiPF₆. Also, the peak height becomes lower by the addition of LiPF₆. These behaviors are also observed by the X‐ray total scattering measurements for the mixture of EC and dimethyl carbonate (DMC) with and without LiPF₆. Also, it is ascertained that such a shrinking is present in EC/DMC electrolytes by means of neutron total scattering. First‐principles calculations on the basis of the density functional theory for isolated EC, EMC, and DMC molecules with the Li⁺ cation confirm that the shrinking of the CO bond is accompanied by the formation of the solvation structure. The observed structural variations induced by adding LiPF₆ will be a good indicator for the formation of the solvation structure.

Unique interstitial Li⁺ and O²⁻/S²⁻ site disorder lower the percolation threshold for 3D Li-ion diffusion in lithium argyrodite Li_6.15Al_0.15Si_1.35S_6−xO_x (LASSO).