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14 results on '"Masashi Okubo"'

1. Lithium-Rich O2-Type Li0.66[Li0.22Ru0.78]O2 Positive Electrode Material.

Author

Hirohito Umeno, Kosuke Kawai, Shin-ichi Nishimura, Daisuke Asakura, Masashi Okubo, and Atsuo Yamada

Subjects
X-ray photoelectron spectroscopy, EMISSION spectroscopy, SOLID solutions, ENERGY density, X-ray absorption, ELECTRODES
Abstract

Increasing the energy density of lithium-ion batteries is an important step towards flexible electricity supply, which can be achieved by developing large-capacity positive electrodes. Lithium-rich oxides have been a longstanding research target because of their large capacity involving extra oxygen-redox reactions. In this work, we report the synthesis, electrochemical properties, electronic structure, and structural evolution of O2-type lithium-rich layered oxide Li1.22-xRu0.78O2. A robust Ru‒O layered framework without Ru migration allows for unveiling the solid-state electrochemistry of O2-type lithium-rich layered oxides with possibility of a large yet stable extra capacity for oxygen-redox reaction. Using a combination of X-ray photoelectron spectroscopy, X-ray absorption/emission spectroscopy, and in situ/ex situ X-ray diffraction, we clarified that O2-Li1.22‒xRu0.78O2 delivers a large capacity of 200 mAh g‒1 in association with Ru5+/Ru4+ and Ru4+/Ru3+ two-electron redox reactions under a solid-solution process, but with no contribution from the extra oxygen-redox reaction. [ABSTRACT FROM AUTHOR]

Published
2022
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3. Interfacial Dissociation of Contact-Ion-Pair on MXene Electrodes in Concentrated Aqueous Electrolytes.

Author

Kijae Kim, Masashi Okubo, and Atsuo Yamada

Subjects
AQUEOUS electrolytes, ENERGY density, ELECTRODES, ENERGY storage, CHEMICAL kinetics, TITANIUM carbide
Abstract

An aqueous supercapacitor is a prospective energy storage device that achieves affordable clean-energy supply. Although recent intensive research on concentrated electrolytes paved the way to improve its low energy density by expanding the narrow electrochemical potential window of water, it was compromised by slow rate capability with respect to the capacitor standard. In this work, to reveal the rate-determining ion-transport mechanism that limits the reaction kinetics of aqueous capacitor electrodes, electrochemical impedance spectroscopy was conducted on layered titanium carbide (MXene) electrodes with concentrated aqueous electrolytes (water-in-salt and hydrate melt). With increasing salt concentration, the dissociation of contact-ion-pair becomes dominant to ion transport both in the bulk electrolyte and at the electrode-electrolyte interface. [ABSTRACT FROM AUTHOR]

Published
2019
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4. Cobalt-Free O2-Type Lithium-Rich Layered Oxides.

Author

de Boisse, Benoit Mortemard, Jeonguk Jang, Masashi Okubo, and Atsuo Yamada

Subjects
COBALT, LITHIUM, LAYER structure (Solids), TRANSITION metal oxides, OXIDATION-reduction reaction, LITHIUM-ion batteries
Abstract

O3-type lithium-rich transition-metal oxides have been attracting interest because of their large specific capacity achieved by additional oxygen-redox reactions. However, their practical application is precluded in part by continuous capacity and voltage fading upon cycling, which mainly originates from layer-to-spinel phase transformation in an O3-type oxide-ion array. In this work, as an attempt to suppress these degradations, we report O2-type cobalt-free lithium-rich layered oxides (Li[Li1/4Mn3/4]O2-Li[Ni1/3Mn2/3]O2 solid solution) which deliver large capacities of 220-250 mAh/g without substantial capacity or voltage fading upon cycling. Our study demonstrates that controlling the O2/O3 polymorphism is a promising approach toward designing large capacity positive electrode materials. [ABSTRACT FROM AUTHOR]

Published
2018
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6. 成人院外心停止患者に対する病院前の高度な気道確保：全国救急蘇生統計コホート研究(Pre–hospital advanced airway management for adults with out–of–hospital cardiac arrest: nationwide cohort study)

Author

(Junichi Izawa), 井澤 純一, (Sho Komukai), 小向 翔, (Koichiro Gibo), 宜保 光一郎, (Masashi Okubo), 大久保 雅史, (Kosuke Kiyohara), 清原 康介, (Chika Nishiyama), 西山 知佳, (Takeyuki Kiguchi), 木口 雄之, (Tasuku Matsuyama), 松山 匡, (Takashi Kawamura), 川村 孝, (Taku Iwami), 石見 拓, (Clifton W Callaway), Clifton W Callaway, and (Tetsuhisa Kitamura), 北村 哲久

Abstract

【目的】院外心停止患者に対する病院前の高度な気道確保は不良な生存・神経学的アウトカムと関連することが，これまでの多くの観察研究で報告されてきた。成人院外心停止患者に対する病院前の高度な気道確保と生存との関連を明らかにすることを目的として本研究を行った。【対象】2014年1月から2016年12月までの本邦の全国救急蘇生統計（ウツタインデータ）を対象に，連続登録された院外心停止成人症例について，心電図の初回記録をもとに「電気ショック適応（心室細動または無脈性心室頻拍）」および「電気ショック非適応（無脈性電気活動または心静止）」の2つのサブコホートに分類した。時間依存性傾向スコアに基づいて同一時点（分）で心肺蘇生時処置として高度な気道確保を受けた患者と高度な気道確保を受けていない患者とを連続的にマッチングさせた。1か月後または1か月以内の退院時の生存割合を主要アウトカムとした。【結果】適格患者310,620名のうち，電気ショック適応群の患者20,516名中8,459名（41.2%）および電気ショック非適応群の患者290,104名中121,890名（42.0%）が心肺蘇生時に高度な気道確保を受けた。時間依存性傾向スコアによる連続マッチングを行った後，電気ショック適応群の患者16,114名および電気ショック非適応群の患者236,042名を同一時点（分）でそれぞれマッチングさせた。電気ショック適応群では，高度な気道確保を受けた患者と受けなかった患者の間で生存割合に差はみられず，それぞれ8,057名中1,546名（19.2%）および8,057名中1,500名（18.6%）であった（調整リスク比1.00，95%信頼区間0.93–1.07）。電気ショック非適応群では，高度な気道確保を受けた患者は受けなかった患者よりも生存割合が高く，それぞれ118,021名中2,696名（2.3%）および118,021名中2,127名（1.8%）であった（調整リスク比1.27，1.20–1.35）。【結論】成人院外心停止患者における時間依存性傾向スコア連続マッチング解析において，電気ショック適応リズムの患者では高度な気道確保と生存に関連がなかったのに対し，電気ショック非適応リズムの患者では高度な気道確保は生存と関連した。 Objective: To determine survival associated with advanced airway management (AAM) compared with no AAM for adults with out–of–hospital cardiac arrest. Design: Cohort study between January 2014 and December 2016. Setting: Nationwide, population based registry in Japan (All–Japan Utstein Registry). Participants: Consecutive adult patients with out–of–hospital cardiac arrest, separated into two sub–cohorts by their first documented electrocardiographic rhythm: shockable (ventricular fibrillation or pulseless ventricular tachycardia) and non–shockable (pulseless electrical activity or asystole). Patients who received AAM during cardiopulmonary resuscitation were sequentially matched with patients at risk of AAM within the same minute on the basis of time dependent propensity scores. Main outcome measures: Survival at one month or at hospital discharge within one month. Results: Of the 310,620 patients eligible, 8,459 (41.2%) of 20,516 in the shockable cohort and 121,890 (42.0%) of 290,104 in the non–shockable cohort received AAM during cardiopulmonary resuscitation. After time dependent propensity score sequential matching, 16,114 patients in the shockable cohort and 236,042 in the non–shockable cohort were matched at the same minute. In the shockable cohort, survival did not differ between patients with AAM and those with no AAM: 1,546/8,057 (19.2%) versus 1,500/8,057 (18.6%) (adjusted risk ratio 1.00, 95% confidence interval 0.93 to 1.07). In the non–shockable cohort, patients with AAM had better survival than those with no AAM: 2,696/118,021 (2.3%) versus 2,127/118,021 (1.8%) (adjusted risk ratio 1.27, 1.20 to 1.35). Conclusions: In the time dependent propensity score sequential matching for out–of–hospital cardiac arrest in adults, AAM was not associated with survival among patients with shockable rhythm, whereas AAM was associated with better survival among patients with non–shockable rhythm.

Published
2020
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