研究者情報

マスター

アカウント（マスター）

• 氏名

  奈須　滉(ナス　アキラ), ナス　アキラ

所属（マスター）

• 理学研究院　化学部門　無機・分析化学分野

所属（マスター）

• 理学研究院　化学部門　無機・分析化学分野

researchmap

プロフィール情報

所属

• 北海道大学, 大学院理学院, 助教

学位

• 博士(工学)（2022年09月 大阪府立大学）

プロフィール情報

• 姓

  奈須, ナス

• 名

  滉, アキラ

• ID各種

  202201000344293865

所属

• 北海道大学, 大学院理学院, 助教

業績リスト

経歴

• 2022年10月 - 現在 北海道大学 大学院理学院 助教

学歴

• 2020年04月 - 2022年09月   大阪府立大学   工学研究科   物質化学系専攻
• 2018年04月 - 2020年03月   大阪府立大学   工学研究科   物質化学系専攻
• 2014年04月 - 2018年03月   大阪府立大学   工学域   物質・化学系学類

論文

• Chemical Compatibility of Solid-State Electrolytes with Hydroflux Cathode-Coating Process

  Kana ONOUE, Tomoyuki WATANABE, Christopher C. JOHN, Akira NASU, Hiroaki KOBAYASHI, Masaki MATSUI

  Electrochemistry 92 7 077002  2024年06月14日
• High-Sodium-Concentration Sodium Oxythioborosilicate Glass Synthesized via Ambient Pressure Method with Sodium Polysulfides

  Tomoya Otono, Akira Nasu, Taichi Asakura, Hiroe Kowada, Kota Motohashi, Masahiro Tatsumisago, Atsushi Sakuda, Akitoshi Hayashi

  Inorganic Chemistry 2024年03月11日
• Heat Treatment of Mechanochemically Prepared Amorphous LiNi0.5Mn1.5O4–Li2SO4 as High-Voltage Positive-Electrode Material

  Neung Kwon, Akira Nasu, Hiroe Kowada, Kota Motohashi, Masahiro Tatsumisago, Atsushi Sakuda, Akitoshi Hayashi

  ACS Applied Energy Materials 2024年03月11日
• Synthesis of High-Sodium-Content Oxythiosilicate Glass Electrolytes Via Sodium Polysulfide

  Tomoya Otono, Akira Nasu, Taichi Asakura, Hiroe Kowada, Kota Motohashi, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  Advanced Sustainable Systems 2024年 

  Sulfide glass electrolytes with high ionic conductivities and formabilities are key materials for practical use in all-solid-state sodium secondary batteries. Both sealing and quenching are considered to be necessary for producing high-alkali-content sulfide glass electrolytes. In this study, the glass-forming ability of sodium thiosilicate glasses is enhanced by adding a small quantity of SiO2. Consequently, high-sodium-content oxythiosilicate glass is synthesized without sealing and quenching processes under Ar atmosphere. The prepared Na4SiS4·0.200SiO2 (molar ratio) glass exhibits ionic conductivity of 4.0 × 10−5 S cm−1 at 25 °C, surpassing that of Na4SiS4 glass. The Na4SiS4·0.200SiO2 glass shows high reduction stability to sodium metal. The all-solid-state Na metal/Na4SiS4·0.200SiO2 glass/Na2.88Sb0.88W0.12S4/TiS2 cell shows a reversible capacity of 140 mAh g−1 for 5 cycles. The amount of H2S gas generated in Na4SiS4·0.0830SiO2 and Na4SiS4·0.200SiO2 glasses is one-tenth that of the Na4SiS4 glass, suggesting increased chemical stability to humidity by incorporating oxygen in the structure. High-sodium-content oxythiosilicate glass with high ionic conductivity, high chemical stability against humidity, and high reduction stability is successfully prepared under ambient pressure without sealing and quenching processes.
• Utilizing reactive polysulfides flux Na 2 S X for the synthesis of sulfide solid electrolytes for all-solid-state sodium batteries

  Akira Nasu

  Energy Storage Materials 2024年
• Trigger of the Highly Resistive Layer Formation at the Cathode–Electrolyte Interface in All-Solid-State Lithium Batteries Using a Garnet-Type Lithium-Ion Conductor

  Kana Onoue, Akira Nasu, Kazuhiko Matsumoto, Rika Hagiwara, Hiroaki Kobayashi, Masaki Matsui

  ACS Applied Materials & Interfaces 2023年11月03日
• Hard Carbon–Sulfide Solid Electrolyte Interface in All-Solid-State Sodium Batteries

  Wataru YOSHIDA, Akira NASU, Kota MOTOHASHI, Masahiro TATSUMISAGO, Atsushi SAKUDA, Akitoshi HAYASHI

  Electrochemistry 91 3 037009 - 037009 2023年03月31日
• Mechanochemical Synthesis and Characterization of K2+xZr1-xYxCl6: Potassium-Ion-Conducting Chloride

  Yuya Okada, Akira Nasu, Takuya Kimura, Hirofumi Tsukasaki, Shigeo Mori, Hamdi Ben Yahia, Kota Motohashi, Atsushi Sakuda, Akitoshi Hayashi

  Chemistry of Materials 2023年 

  K-ion batteries are attracting attention as rechargeable batteries following Li-ion and Na-ion batteries. However, their safety is of concern owing to the use of organic electrolytes. The use of solid electrolytes instead of organic electrolytes can resolve this problem. Chloride solid electrolytes have attracted attention in recent years as Li- and Na-ion conductors, but reports on chloride K-ion conductors have been scarce. In this study, new K-ion-conducting chlorides, K2+xZr1-xYxCl6 (x = 0-1), were prepared by a mechanochemical method. The X-ray powder diffraction (XRPD) patterns of the prepared solid electrolytes exhibited broad Bragg peaks, and the high-resolution transmission electron microscopy observations revealed the presence of nanocrystals dispersed in amorphous matrixes. New crystalline phases, closely related to monoclinic K2TeCl6, were precipitated in the K2+xZr1-xYxCl6 matrixes at x = 0-0.4. The Rietveld refinements of the XRPD patterns for the new phases revealed that the excess of K, introduced by Y substitution, occupied the vacant B′ octahedral site of the cation-deficient double perovskite A2BB′X6 structure. The conductivity at 25 °C of the K2+xZr1-xYxCl6 chlorides exceeded 10-7 S cm-1 at x = 0-0.4, and a maximum conductivity of 9.2 × 10-7 S cm-1 was achieved at x = 0.3. Heat treatment above 400 °C of the K2+xZr1-xYxCl6 electrolyte with x = 0.3 resulted in crystallization of the amorphous components, decomposition of the phase into a mixture of K2ZrCl6 and K3YCl6, and a decrease of the ionic conductivity. In addition to the K concentration and crystalline phase in the electrolytes, the amorphous components also play a key role in the high ionic conductivity of the K2+xZr1-xYxCl6 chlorides.
• Mechanochemical synthesis of Na3NbS4 metastable phase as positive electrode materials for all-solid-state sodium batteries

  Akira Nasu, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  Journal of the Ceramic Society of Japan 130 9 789 - 793 2022年09月01日 

  Transition metal sulfides have been reported to be active materials with high capacities by using anionic redox reactions. Modifying the structure to favor the extraction/insertion of sodium is beneficial in achieving the theoretical capacity of these sulfides. In this study, we synthesized three new phases of Na3NbS4 via a mechanochemical (MC) process. Under moderate MC conditions, amorphous Na3NbS4 was obtained. Under harsher MC conditions, metastable phases I and II of Na3NbS4 were obtained at different process times of 10 and 40 h, respectively. The conductivities of the three Na3NbS4 materials were higher than that of orthorhombic Na3NbS4. In particular, the metastable phase I of Na3NbS4 showed the highest conductivity of 3.2 © 1016 S cm11, and the all-solid-state sodium cells with metastable phase I as an electrode active material showed the highest capacity of 240 mAh g11. Thus, the MC process is useful for synthesizing positive electrode active materials on transition metal sulfides with an advantageous structure to achieve a high capacity.
• Iron Sulfide Na2FeS2 as Positive Electrode Material with High Capacity and Reversibility Derived from Anion-Cation Redox in All-Solid-State Sodium Batteries

  Akira Nasu, Atsushi Sakuda, Takuya Kimura, Minako Deguchi, Akihisa Tsuchimoto, Masashi Okubo, Atsuo Yamada, Masahiro Tatsumisago, Akitoshi Hayashi

  SMALL 18 42 2022年09月 

  It is desirable for secondary batteries to have high capacities and long lifetimes. This paper reports the use of Na2FeS2 with a specific structure consisting of edge-shared and chained FeS4 as the host structure and as a high-capacity active electrode material. An all-solid-state sodium cell that uses Na2FeS2 exhibits a high capacity of 320 mAh g(-1), which is close to the theoretical two-electron reaction capacity of 323 mAh g(-1), and operates reversibly for 300 cycles. The excellent electrochemical properties of all-solid-state sodium cells are derived from the anion-cation redox and rigid host structure during charging/discharging. In addition to the initial one-electron reaction of NaxFeS2 (1 <= x <= 2) activated Fe2+/Fe3+ redox as the main redox center, the reversible sulfur redox further contributes to the high capacity. Although the additional sulfur redox affects the irreversible crystallographic changes, stable and reversible redox reactions are observed without capacity fading, owing to the local maintenance of the chained FeS4 in the host structure. Sodium iron sulfide Na2FeS2, which combines low-cost elements, is one of the candidates that can meet the high requirements of practical applications.
• Amorphous Positive Electrode Materials Prepared Using LiMn(1.5)Ni(0.5)O4 and Lithium Oxyacid Salts

  Neung Kwon, Akira Nasu, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  CHEMISTRY LETTERS 51 8 815 - 818 2022年08月 

  LiNi0.5Mn1.5O4 is an attractive choice for a high-voltage positive electrode material for all-solid-state batteries. However, its use in all-solid-state batteries is challenging because of low ionic conductivity. In this study, we synthesized new amorphous electrode materials from LiMn1.5Ni0.5O4 and lithium oxyacid salts. The synthesized amorphous electrodes exhibited higher ionic conductivity and capacity than a LiMn1.5Ni0.5O4 crystal in both liquid-and solid-type cells. Among these electrodes, amorphous 80LiMn(1.5)Ni(0.5)O(4).20Li3PO(4) (mol %) demonstrated a high reversible capacity of 220 mAh g(-1)in a liquid-type cell.
• Preparation and characterization of Na2.88Sb0.88W0.12S4-xOx solid electrolyte

  Takuma Takayanagi, Akira Nasu, Fumika Tsuji, Kota Motohashi, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 130 7 498 - 503 2022年07月 

  For the practical application of all-solid-state batteries, it is necessary to improve the performance of the solid electrolytes. We previously reported the fabrication of Na2.88Sb0.88W0.12S4, which showed the highest ionic conductivity among Na+ conducting sulfide solid electrolytes. In this study, we focused on the anion substitution of Na2.88Sb0.88W0.12S4 and evaluated oxygen substitution. Samples of Na2.88Sb0.88W0.12S4-xOx (0 <= x <= 0.5) were fabricated by a mechanochemical process and subsequent heat treatment, and structural analysis and electrochemical evaluation were performed. The solid solution of oxygen was found to proceed in the range of x <= 0.3. The oxygen substitution decreased the ionic conductivity, but it maintained a high ionic conductivity of more than 10(-3) S cm(-1). The reduction tolerance was improved by the oxygen substitution based on cyclic voltammetry measurements. An all-solid-state Na-Sn/TiS2 cell using the Na2.88Sb0.88W0.12S3.7O0.3 electrolyte operated at room temperature. (C) 2022 The Ceramic Society of Japan. All rights reserved.
• Na2S-NaI solid solution as positive electrode in all-solid-state Na/ S batteries

  Yushi Fujita, Akira Nasu, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  JOURNAL OF POWER SOURCES 532 2022年06月 

  All-solid-state sodium-sulfur (Na/S) batteries are promising next-generation batteries with high safety and high energy density. Sodium sulfide (Na2S) has application as active material in positive electrodes owing to its advantages such as low cost, low toxicity, and a large theoretical capacity. However, the electronic and sodium ion conductivities of Na2S are significantly low, and ascertaining the entire contribution of the active materials to cell capacities is challenging. Therefore, facilitating an electronic and ionic conduction path in the positive electrode is essential. In this study, Na2S was mixed with sodium iodide (NaI) via a mechanochemical process and was used as an active material in an all-solid-state Na/S battery. Consequently, a Na2S-NaI solid solution was formed, and the ionic conductivity of Na2S-NaI increased by five orders of magnitude compared to that of Na2S. Na2S-NaI showed large charge-discharge capacities and cycle capability. In particular, 90Na(2)S.10NaI showed a large capacity and high cycle efficiency, and 94% of Na2S acted as an active material. The result of this study leads to the development of all-solid-state Na/S batteries with high capacities, high rates, and high cycles.
• Room-Temperature Preparation of All-Solid-State Lithium Batteries Using TiO(2 )Anodes and Oxide Electrolytes

  Hiroyuki Usui, Yasuhiro Domi, Shin-ichiro Izaki, Akira Nasu, Atsushi Sakuda, Akitoshi Hayashi, Hiroki Sakaguchi

  JOURNAL OF PHYSICAL CHEMISTRY C 126 25 10320 - 10326 2022年06月 

  ABSTRACT: We tried to prepare solid-state batteries consisting of TiO2 anodes and a Li3BO3???Li2SO4???Li2CO3 solid electrolyte only by room-temperature pressing without any sintering process. The solid-state batteries successfully operated at 90 ??C and showed reversible capacity in the range of 278???331 mA h g???1 in the first cycles at 0.01C. In addition to this, the rate capability was remarkably improved by the doping of Nb or Ta into TiO2: the doped TiO2 electrodes exhibited a capacity of 140 mA h g???1 at 0.1C, whereas the undoped TiO2 showed only 10 mA h g???1. The charge-transfer resistance of TiO2 was reduced by the doping of Nb or Ta. The improvement in the anode performance was attributed to the improved electronic conductivity and the expanded interlayer distance by doping. These results demonstrated for the first time that the oxide anodes can operate in bulk-type oxide-based solid-state batteries prepared only by room-temperature pressing.
• Formation of Passivate Interphases by Na3BS3-Glass Solid Electrolytes in All-Solid-State Sodium-Metal Batteries

  Akira Nasu, Takeaki Inaoka, Fumika Tsuji, Kota Motohashi, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  ACS APPLIED MATERIALS & INTERFACES 14 21 2022年05月 

  Interphase formation at the interface between a solid electrolyte and negative electrode is one of the main factors limiting the practical use of all-solid-state sodium batteries. Sulfide-type solid electrolytes with group 15 elements (P and Sb) exhibit high ductility and ionic conductivity, comparable to those of organic liquid electrolytes. However, the electronically conductive interphase formed at the interface between Na3PS4 and sodium metal increases the cell resistance and deteriorates its electrochemical properties. Contrarily, Na3BS3, containing boron as an electrochemically inert element, forms an electronically insulating thin passivate interphase, facilitating reversible sodium plating and stripping. Sodium-metal symmetric cells with Na3BS3 exhibit steady operation over 1000 cycles. Thus, reduction-stable solid electrolytes can be developed by substitution with an electrochemically inert element versus sodium.
• Mechanochemical synthesis of amorphous MoSx (x=3, 4, 5, 6, and 7) electrode for all-solid-state sodium battery

  Gaku Shirota, Akira Nasu, Minako Deguchi, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 130 4 308 - 312 2022年04月 

  All-solid-state sodium secondary batteries have garnered significant attention as next-generation batteries with high safety. To realize an all-solid-state sodium secondary battery with a high energy density, it is necessary to develop a high-capacity electrode active material. In this study, we prepared amorphous molybdenum polysulfide (a-MoSx, x = 3-7) using a mechanochemical process as electrode active material in all-solid-state cells using Na3PS4 sulfide electrolyte. In all-solid-state cells, a-MoS3, a-MoS4, a-MoS5, a-MoS6, and a-MoS7 showed high reversible capacities of 260, 330, 470, 540, and 510 mAh g(-1), respectively. X-ray photoelectron spectroscopy analyses suggested that the discharge-charge reaction in a-MoSx proceeds mainly by anion redox with dissociation and formation of disulfide bonds. Amorphous sulfur-rich MoSx is thus a promising electrode active material with high capacity in all-solid-state sodium batteries. (C) 2022 The Ceramic Society of Japan. All rights reserved.
• Molybdenum polysulfide electrode with high capacity for all-solid-state sodium battery

  Gaku Shirota, Akira Nasu, Minako Deguchi, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  SOLID STATE IONICS 376 2022年03月 

  All-solid-state sodium secondary batteries have attracted significant attention as an alternative for post-lithium-ion batteries. However, to obtain all-solid-state sodium secondary batteries with high-energy density, it is necessary to develop a high-capacity positive electrode material. In this study, two types of amorphous (a-)MoSx (x & nbsp;? 6) active electrode materials were prepared using a mechanochemical (MC) process and through the thermal decomposition (TD) of (NH4)(2)Mo2S12.2H(2)O. Herein, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) analyses were conducted, and the results revealed significantly different local structures of a-MoSx (MC) and a-MoSx (TD). The all-solid-state sodium cells with a-MoSx (MC) and a-MoSx (TD) possessed high reversible capacities of 510 and 690 mAh g(-1), as well as high-capacity retention rates of 80% and 92% for the 2nd to 30th cycles, respectively. XPS analysis of the discharge-charge products further suggested that dissociation and formation of disulfide bonds occurred reversibly during the discharge-charge reaction. This study shows that a-MoSx (MC) and a-MoSx (TD) are promising active electrode materials for all-solid-state sodium batteries.
• Sodium-Ion Conducting Solid Electrolytes in the Na2S-In2S3 System

  Kota Motohashi, Akira Nasu, Takuya Kimura, Chie Hotehama, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  ELECTROCHEMISTRY 90 6 2022年 

  The development of solid electrolytes is necessary for practical applications of all-solid-state Na-ion batteries. In this study, we systematically developed sulfide Na-ion conductors with central In cations, prepared by solid-state reaction and mechanochemical methods. Thermodynamically stable crystals of Na5InS4 and NaInS2 were obtained by the solid-state reaction method, whereas amorphous and/or metastable phases were produced by the mechanochemical method. Two new metastable phases, Na5InS4 and NaInS2, are expected to be examined in the future as end-members of sulfide Na-ion conductors with central In cations. (C) The Author(s) 2022. Published by ECSJ.
• Mechanochemical Synthesis of Pyrite Ni1-xFexS2 Electrode for All-solid-state Sodium Battery

  Gaku Shirota, Akira Nasu, Atsushi Sakuda, Minako Deguchi, Kota Motohashi, Masahiro Tatsumisago, Akitoshi Hayashi

  ELECTROCHEMISTRY 90 3 2022年 

  All-solid-state sodium secondary batteries are expected to be low-cost, next-generation batteries. NiS2 and FeS2 are potential candidates as positive electrode materials owing to their high theoretical capacities. However, it is difficult to achieve sufficient capacity with bulk FeS2. In this study, pyrite Ni1-xFexS2 (x = 0, 0.3, 0.5, 0.7, 0.9, and 1) electrodes are prepared by a mechanochemical process. The all-solid-state sodium cells with Ni1-xFexS2 show higher discharge-charge potentials than those with NiS2, and higher capacities than those with FeS2. In addition, Ni1-xFexS2 exhibits a higher rate performance than those of NiS2 and FeS2. The all-solid-state cells using Ni1-xFexS2 (x = 0.3, 0.5, and 0.7) are discharged and charged with a high capacity of approximately 390 mAh g(-1), without significant capacity fading for at least 30 cycles. The solid-solution formation of NiS2 and FeS2 results in lower material cost, higher rate performance, higher discharge-charge potential than those of NiS2, and higher capacity than that of FeS2. Pyrite Ni1-xFexS2 is a promising positive electrode material for all-solid-state sodium secondary batteries.[GRAPHICS]. (C) The Author(s) 2022. Published by ECSJ.
• Mechanochemically Prepared Highly Conductive Na2.88Sb0.88W0.12S4-NaI Composite Electrolytes for All-Solid-State Sodium Battery

  Takuma Takayanagi, Akira Nasu, Fumika Tsuji, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  ELECTROCHEMISTRY 90 4 2022年 

  Solid electrolytes with high ionic conductivity, high formability, and high electrochemical properties are required to improve the performance of all-solid-state sodium batteries. In this study, we focus on a combination of Na2.88Sb0.88W0.12S4 and NaI for preparing composite electrolytes Na2.88Sb0.88W0.12S4 center dot xNaI, and investigate their crystal structures, microstructures, and electrochemical properties. NaI is uniformly dispersed in the composites without forming a solid solution with Na2.88Sb0.88W0.12S4. Na2.88Sb0.88W0.12S4 center dot 0.50NaI shows a high ionic conductivity of 3.6 x 10(-2) S cm(-1) after sintering at 275 degrees C for only 1.5 h. The charge-discharge characteristics of all-solid-state cells using the Na2.88Sb0.88W0.12S4 center dot xNaI composite are also improved. (c) The Author(s) 2022. Published by ECSJ. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium provided the original work is properly cited.
• Crystallization behaviors in superionic conductor Na3PS4

  Hiroshi Nakajima, Hirofumi Tsukasaki, Jiong Ding, Takuya Kimura, Takumi Nakano, Akira Nasu, Akihiko Hirata, Atsushi Sakuda, Akitoshi Hayashi, Shigeo Mori

  JOURNAL OF POWER SOURCES 511 2021年11月 

  All-solid-state batteries using sodium are promising candidates for next-generation rechargeable batteries due to the limited lithium resources. A practical sodium battery requires an electrolyte with high conductivity. Cubic Na3PS4 exhibiting high conductivity of over 10-4 S cm- 1 is obtained by crystallizing amorphous Na3PS4 synthesized by ball milling. Amorphous Na3PS4 crystallizes in a cubic structure and then is transformed into a tetragonal phase upon heating. In this study, in situ observation by transmission electron microscopy demonstrates that the crystallite size drastically increases during the transition from the cubic phase to the tetragonal phase. Moreover, an electron diffraction analysis reveals that amorphous domains and nano-sized crystallites coexist in the cubic Na3PS4 specimen, while the tetragonal phase contains micro-sized crystallites. The nanosized crystallites and the composite formed by crystallites and amorphous domains are most likely responsible for the increase in conductivity in the cubic Na3PS4 specimens.
• Mechanochemical synthesis and characterization of Na3-xP1-xWxS4 solid electrolytes

  Fumika Tsuji, Akira Nasu, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  JOURNAL OF POWER SOURCES 506 2021年09月 

  All-solid-state sodium batteries are attracting attention as next-generation batteries, owing to their improved safety and abundance of sodium resources. To realize all-solid-state sodium batteries, solid electrolytes with high sodium-ion conductivities are required. In this study, Na3PS4 electrolytes with partial substitution of P5+ with W6+ were investigated. The Na3-xP1-xWxS4 sulfide-based solid electrolytes were prepared via a mechanochemical process and consecutive heat treatment. The Na2.85P0.85W0.15S4 electrolyte with Na vacancies exhibited an ionic conductivity of 8.8 x 10(-3) S cm(-1) at 25 degrees C, which was higher than that of Na3PS4 solid electrolyte. The all-solid-state batteries (Na-Sn/Na2.85P0.85W0.15S4/TiS2) exhibited a reversible capacity of 140 mA h g(-1) at a current density of 0.038 mA cm(-2) and retained the capacity of 115 mAh g(-1) for 40 cycles at 0.130 mA cm(-2) at 25 degrees C. The Na3-xP1-xWxS4 samples prepared via mechanochemistry are homogeneous electrolytes free of crystalline WS2 impurities and are effective for application to all-solid-state sodium batteries.
• Electrode performance of amorphous MoS3 in all-solid-state sodium secondary batteries

  Gaku Shirota, Akira Nasu, Minako Deguchi, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  JOURNAL OF POWER SOURCES ADVANCES 10 2021年08月 

  All-solid-state Na-S secondary batteries that use sodium and sulfur, both available in abundance, are the most attractive next-generation batteries. In this study, two types of amorphous MoS3 (a-MoS3) were prepared as electrode active materials for use in all-solid-state sodium secondary batteries using the thermal decomposition (TD) of (NH4)(2) MoS4 and mechanochemical (MC) processes, denoted a-MoS3 (TD) and a-MoS3 (MC), respectively. X-ray diffraction, thermogravimetric-differential thermal analysis, and X-ray photoelectron spectroscopy (XPS) analyses revealed that a-MoS3 (TD) and a-MoS3 (MC) had different local structures. The a-MoS3 (TD) and a-MoS3 (MC) electrodes showed high reversible capacities of 310 mAh g(-1) and 260 mAh g(-1) , respectively, for five cycles in all-solid-state sodium secondary batteries. XPS analysis of the discharge-charge products suggested that the dissociation and formation of disulfide bonds occurred during the discharge-charge reaction. The results show that a-MoS3 is a promising active electrode material for all-solid-state sodium batteries.
• Preparation and characterization of sodium-ion conductive Na3BS3 glass and glass-ceramic electrolytes

  Fumika Tsuji, Akira Nasu, Chie Hotehama, Atsushi Sakuda, Masahiro Tatsumisago, Akitoshi Hayashi

  MATERIALS ADVANCES 2 5 1676 - 1682 2021年03月 

  In order to find suitable solid electrolytes for all-solid-state sodium batteries, sulfide electrolytes composed of tetrahedral structural units such as PS4, SnS4 and SbS4 have been widely studied. In this paper, the ionic conductivities of Na(3)BS(3)ortho-thioborate electrolytes with triangular BS3 units are firstly reported. Na3BS3 glass was prepared via a mechanochemical process from crystalline Na3BS3 (monoclinic phase). The crystalline Na3BS3 was pre-synthesized from a mixture of Na2S, B, and S due to the instability of the B2S3 compound. A new metastable phase of trigonal Na3BS3 was precipitated as the primary phase by crystallization of the Na3BS3 glass. The prepared glass-ceramic electrolyte showed a higher ionic conductivity than the monoclinic Na3BS3 phase. The Na3BS3 glass showed the highest conductivity of 1.1 x 10(-5) S cm(-1), which was higher than that of conventional Na3PS4 glass. Futhermore, the Na3BS3 glass showed a superior formability and electrochemical stability to Na15Sn4 negative electrode. An all-solid-state cell with the Na3BS3 glass as an electrolyte successfully operated as a secondary battery at 60 degrees C. It is concluded that the Na3BS3 glass with triangular structural units has appropriate properties as a solid electrolyte for application to all-solid-state sodium batteries. The results of this study extend research on multi-component sulfide electrolytes with triangular BS3 structural units and contribute to the development of solid electrolytes for all-solid-state batteries.
• Mechanochemical synthesis of cubic rocksalt Na2TiS3 as novel active materials for all-solid-state sodium secondary batteries

  Akira Nasu, Misae Otoyama, Atsushi Sakuda, Akitoshi Hayashi, Masahiro Tatsumisago

  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 127 8 514 - 517 2019年08月 

  Mechanochemical (MC) process is one of the most effective methods to produce amorphous and cation disordered electrode active materials. We individually synthesized amorphous and cation disordered cubic rocksalt Na2TiS3 by controlling the preparation conditions of the MC process. Cubic rocksalt Na2TiS3 and ordered monoclinic Na2TiS3 were also obtained via the heat treatment of amorphous Na2TiS3. The all-solid-state cell with cubic rocksalt Na2TiS3 showed a high reversible capacity of 270 mAh g(-1), which corresponds to the theoretical capacity of Na2TiS3. The cell maintained the capacity for more than 30 cycles, indicating that the active materials can endure long operation life. The MC methods for transition metal sulfides and the search for ordered monoclinic polymorphs are necessary for the pursuit of novel electrode materials. (C) 2019 The Ceramic Society of Japan. All rights reserved.
• Amorphous Na2TiS3 as an Active Material for All-solid-state Sodium Batteries

  Akira Nasu, Misae Otoyama, Atsushi Sakuda, Akitoshi Hayashi, Masahiro Tatsumisago

  CHEMISTRY LETTERS 48 3 288 - 290 2019年03月 

  Amorphous transition metal polysulfides are promising high capacity electrode active materials for sodium secondary batteries. Here we report the superior electrode performance of amorphous Na2TiS3. Crystalline (c-) and amorphous (a-) Na2TiS3 were prepared by solid phase reaction with heat treatment and mechanochemical reaction, respectively. a-Na2TiS3 showed 10 fold higher ionic conductivity (1.5 x 10(-6) S cm(-1)) than that of c-Na2TiS3. The all-solid-state cells using c-Na2TiS3 and a-Na2TiS3 showed reversible capacities of 110 mAhg(-1) and 250 mAhg(-1), respectively. Amorphization of Na2TiS3 is a powerful way to improve electrode performance in all-solid-state sodium secondary batteries.

MISC

• 多硫化ナトリウムを利用したNa_2.88Sb_0.88W_0.12S₄固体電解質の常圧合成

  音野智哉, 城田岳, 奈須滉, 本橋宏大, 作田敦, 林晃敏 電池討論会PDF要旨集(CD-ROM) 63rd 2022年
• 多硫化ナトリウムを利用したNa₃BS₃ガラス電解質の合成プロセスの開発

  音野智哉, 城田岳, 奈須滉, 本橋宏大, 作田敦, 林晃敏 化学電池材料研究会ミーティング講演要旨集 23rd (CD-ROM) 2022年

所属学協会

• 日本セラミックス協会   電気化学会   

共同研究・競争的資金等の研究課題

• 多様な元素を含む未踏領域における耐還元性を有する硫化物固体電解質の探索

  日本学術振興会：科学研究費助成事業

  研究期間 : 2024年04月 -2027年03月 

  代表者 : 奈須 滉
• 遷移金属硫化物におけるナトリウム含有型活物質モデルの新規構築

  日本学術振興会：科学研究費助成事業 特別研究員奨励費

  研究期間 : 2020年04月 -2023年03月 

  代表者 : 奈須 滉

   

  ナトリウム二次電池の正極活物質の中でも、構成元素として豊富で普遍的な元素を含む鉄系硫化物FeS2は、安価かつ実用的な材料として報告されている。しかし、初期放電時の不可逆な構造変化や、構造中のナトリウムイオンの拡散の遅さから高出力化は容易ではない。本研究では、ナトリウムイオンが拡散可能な結晶構造を有し、実験的にも10-6 S cm-1程度のイオン伝導性を示す材料としてナトリウム含有型の鉄系硫化物Na2FeS2に着目し、全固体ナトリウム電池への適用とその充放電機構について解析した。まず、Na2FeS2の全固体電池への適用では、300サイクル以上の間、300 mAh g-1の高容量を保持することを明らかにした。高い電極特性を示す要因の特定のために、XRD測定、XPS測定、57Fe Moessbauer測定を用いて、結晶構造変化と電子状態変化を解析した。その結果、充放電中にカチオンである鉄、アニオンの硫黄のどちらもが充放電に関与しており、酸化還元対の増加によって、高容量が実現していることが明らかになった。また、Na2FeS2の結晶構造中で、陵共有によって鎖状となっているFeS4四面体が充電・放電を通して維持されることで、イオン伝導経路が維持されていることが分かった。以上の結果を踏まえて、正極中のイオン伝導助剤である固体電解質を利用することなく、Na2FeS2のみを圧粉成形することで正極とした全固体電池の構築・作動に成功し、電池全体の高エネルギー密度化を実現した。