岡本 範彦*; 吉迫 大輝*; 市坪 哲
Energy Storage Materials, 61, p.102912_1 - 102912_9, 2023/08
Layered manganese dioxide (birnessite) that contains K cations and water molecules at interlayers exhibits reversible heat storage properties via a water-intercalation mechanism (0.5 mol HO per KMnO). However, a certain amount of an irreversible capacity of water intercalation is observed after the initial thermal cycle, which limits the reversibly available energy density of the material for the subsequent cycles. In this study, crystal structures of the K-containing birnessite, KMnO, was analyzed before and after heat treatment, by electron diffraction and atomic-resolution scanning transmission electron microscopy, to elucidate the origin of the initial irreversible capacity (0.83 mol per KMnO).
下川 航平*; 松原 翔吾*; 河口 智也*; 岡本 章玄*; 市坪 哲
Chemical Communications, 59(51), p.7947 - 7950, 2023/06
Spinel oxides can be a promising high-potential cathode material of photo-rechargeable batteries. However, LiMnMO (M = Mn) has a difficulty in a rapid degradation during charge/discharge under the illumination of UV-visible light. In this study, various spinel-oxide materials by modifying the composition (M = Fe, Co, Ni, Zn) were investigated to demonstrate photocharging in a water-in-salt aqueous electrolyte. LiMnFeO showed a substantially higher discharge capacity compared to that of LiMnO after long-term photocharging owing to enhanced stability under illumination. The result of this work provides fundamental design guidelines of spinel-oxide cathode materials to develop photo-rechargeable batteries.
Ye, X.*; 下川 航平*; 毛塚 有飛*; 畠山 拓也*; Li, H.*; 市坪 哲
Journal of Physical Chemistry C, 127(11), p.5210 - 5218, 2023/03
In this study, wide-range compositions in Mg-Zn-Mn oxide systems were investigated to understand its phase stability for the development of high-energy-density rechargeable Mg batteries. The obtained results showed that the stability of the spinel structure can be significantly improved by compositionally incorporating stable XO (X = Zn, Mg) with -MnO. In particular, (i) the equimolar mixing of XO and MnO is essential to obtain a single-phase cubic spinel structure and (ii) a higher Zn/Mg ratio is effective for preventing the formation of an irreversible rock salt phase to decrease the overpotential during discharge/charge cycling.
下川 航平*; 松原 翔吾*; 岡本 章玄*; 市坪 哲
Chemical Communications, 58(69), p.9634 - 9637, 2022/09
Photocharging of high-potential spinel LiMnO is demonstrated by using a water-in-salt electrolyte and TiO nanoparticles. In a developed half-cell system with an electron acceptor, Li extraction from LiMnO proceeds under the illumination of UV-visible light at an estimated rate of c.a. 23 mA g. This work paves the way for highpotential cathode materials in photo-rechargeable batteries.
Wei, D.*; Wang, L.*; Zhang, Y.*; Gong, W.; 都留 智仁; Lobzenko, I.; Jiang, J.*; Harjo, S.; 川崎 卓郎; Bae, J. W.*; et al.
Acta Materialia, 225, p.117571_1 - 117571_16, 2022/02
Recently-developed high-entropy alloys (HEAs) containing multiple principal metallic elements have ex-tended the compositional space of solid solutions and the range of their mechanical properties. Here we show that the realm of possibilities can be further expanded through substituting the constituent metals with metalloids, which are desirable for tailoring strength/ductility because they have chemical interactions and atomic sizes distinctly different from the host metallic elements. Specifically, the metalloid substitution increases local lattice distortion and short-range chemical inhomogeneities to elevate strength, and in the meantime reduces the stacking fault energy to discourage dynamic recovery and encourage defect accumulation via partial-dislocation-mediated activities. These impart potent dislocation storage to improve the strain hardening capability, which is essential for sustaining large tensile elongation. As such, metalloid substitution into HEAs evades the normally expected strength-ductility trade-off, enabling an unusual synergy of high tensile strength and extraordinary ductility for these single-phase solid solutions.
木村 哲也*; 有井 祥夫; 市坪 浩二; 土田 佳裕
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