Hideyuki Komatsu
Kyoto University
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Featured researches published by Hideyuki Komatsu.
Journal of Materials Chemistry | 2016
Keiji Shimoda; Taketoshi Minato; Koji Nakanishi; Hideyuki Komatsu; Toshiyuki Matsunaga; Hajime Tanida; Hajime Arai; Yoshio Ukyo; Yoshiharu Uchimoto; Zempachi Ogumi
The oxidation/reduction behaviours of lattice oxygen and transition metals in a Li-rich manganese-based layered oxide Li[Li0.25Ni0.20Mn0.55]O1.93 are investigated by using hard X-ray photoelectron spectroscopy (HAX-PES). By making use of its deeper probing depth rather than in-house XPS analyses, we clearly confirm the formation of O− ions as bulk oxygen species in the active material. They are formed on the 1st charging process as a charge compensation mechanism for delithiation and decrease on discharging. In particular, the cation–anion dual charge compensation involving Ni and O ions is suggested during the voltage slope region of the charging process. The Ni ions in the material are considered to increase the capacity delivered by a reversible anion redox reaction with the suppression of O2 gas release. On the other hand, we found structural deterioration in the cycled material. The O− species are still observed but are electrochemically inactive during the 5th charge–discharge cycle. Also, the oxidation state of Ni ions is divalent and inactive, although that of Mn ions changes reversibly. We believe that this is associated with the structural rearrangement occurring after the activation process during the 1st charging, leading to the formation of spinel- or rocksalt-like domains over the sub-surface region of the particles.
Physical Chemistry Chemical Physics | 2016
Ikuma Takahashi; Hajime Arai; Haruno Murayama; Kenji Sato; Hideyuki Komatsu; Hajime Tanida; Yukinori Koyama; Yoshiharu Uchimoto; Zempachi Ogumi
LiNi0.5Mn1.5O4 (LNMO) is a promising positive electrode material for lithium ion batteries because it shows a high potential of 4.7 V vs. Li/Li(+). Its charge-discharge reaction includes two consecutive phase transitions between LiNi0.5Mn1.5O4 (Li1) ↔ Li0.5Ni0.5Mn1.5O4 (Li0.5) and Li0.5 ↔ Ni0.5Mn1.5O4 (Li0) and the complex transition kinetics that governs the rate capability of LNMO can hardly be analyzed by simple electrochemical techniques. Herein, we apply temperature-controlled operando X-ray absorption spectroscopy to directly capture the reacting phases from -20 °C to 40 °C under potential step (chronoamperometric) conditions and evaluate the phase transition kinetics using the apparent first-order rate constants at various temperatures. The constant for the Li1 ↔ Li0.5 transition (process 1) is larger than that for the Li0.5 ↔ Li0 transition (process 2) at all the measured temperatures, and the corresponding activation energies are 29 and 46 kJ mol(-1) for processes 1 and 2, respectively. The results obtained are discussed to elucidate the limiting factor in this system as well as in other electrode systems.
Journal of Physical Chemistry Letters | 2016
Toshiyuki Matsunaga; Hideyuki Komatsu; Keiji Shimoda; Taketoshi Minato; Masao Yonemura; Takashi Kamiyama; Shunsuke Kobayashi; Takeharu Kato; Tsukasa Hirayama; Yuichi Ikuhara; Hajime Arai; Yoshio Ukyo; Yoshiharu Uchimoto; Zempachi Ogumi
We examined the crystal structures of Li2(NixMn1-x)O3(-δ) (x = 0, 1/10, 1/6, and 1/4) to elucidate the relationship between the structure and electrochemical performance of the compounds using neutron and synchrotron X-ray powder diffraction analyses in combination. Our examination revealed that these crystals contain a large number of stacking faults and exhibit significant cation mixing in the transition-metal layers; the cation mixing becomes significant with an increase in the Ni concentration. Charge-discharge measurements showed that the replacement of Mn with Ni lowers the potential of the charge plateau and leads to higher charge-discharge capacities. From a topological point of view with regard to the atomic arrangement in the crystals, it is concluded that substituting Mn in Li2MnO3 with Ni promotes the formation of smooth Li percolation paths, thus increasing the number of active Li ions and improving the charge-discharge capacity.
Advanced Energy Materials | 2015
Hideyuki Komatsu; Hajime Arai; Yukinori Koyama; Kenji Sato; Takeharu Kato; Ryuji Yoshida; Haruno Murayama; Ikuma Takahashi; Yuki Orikasa; Katsutoshi Fukuda; Tsukasa Hirayama; Yuichi Ikuhara; Yoshio Ukyo; Yoshiharu Uchimoto; Zempachi Ogumi
Journal of Physical Chemistry C | 2015
Keiji Shimoda; Miwa Murakami; Hideyuki Komatsu; Hajime Arai; Yoshiharu Uchimoto; Zempachi Ogumi
Chemistry of Materials | 2016
Toshiyuki Matsunaga; Hideyuki Komatsu; Keiji Shimoda; Taketoshi Minato; Masao Yonemura; Takashi Kamiyama; Shunsuke Kobayashi; Takeharu Kato; Tsukasa Hirayama; Yuichi Ikuhara; Hajime Arai; Yoshio Ukyo; Yoshiharu Uchimoto; Zempachi Ogumi
Journal of Physical Chemistry C | 2016
Ikuma Takahashi; Katsutoshi Fukuda; Tomoya Kawaguchi; Hideyuki Komatsu; Masatsugu Oishi; Haruno Murayama; Masaharu Hatano; Takayuki Terai; Hajime Arai; Yoshiharu Uchimoto; Eiichiro Matsubara
Chemistry of Materials | 2017
Yukinori Koyama; Takeshi Uyama; Yuki Orikasa; Takahiro Naka; Hideyuki Komatsu; Keiji Shimoda; Haruno Murayama; Katsutoshi Fukuda; Hajime Arai; Eiichiro Matsubara; Yoshiharu Uchimoto; Zempachi Ogumi
Journal of Physical Chemistry C | 2018
Hideyuki Komatsu; Taketoshi Minato; Toshiyuki Matsunaga; Keiji Shimoda; Tomoya Kawaguchi; Katsutoshi Fukuda; Koji Nakanishi; Hajime Tanida; Shunsuke Kobayashi; Tsukasa Hirayama; Yuichi Ikuhara; Hajime Arai; Yoshio Ukyo; Yoshiharu Uchimoto; Eiichiro Matsubara; Zempachi Ogumi
PRiME 2016/230th ECS Meeting (October 2-7, 2016) | 2016
Hideyuki Komatsu; Taketoshi Minato; Toshiyuki Matsunaga; Keiji Shimoda; Tomoya Kawaguchi; Katsutoshi Fukuda; Koji Nakanishi; Hajime Arai; Yoshiharu Uchimoto; Eiichiro Matsubara; Zempachi Ogumi