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5. Structural analysis of sulfuric acid solutions containing Ti and Mn using x-ray diffraction, x-ray absorption fine structure, and molecular dynamics simulation.

Author

Tokuda, Kazuya, Iihara, Junji, Saito, Yoshihiro, Masuno, Atsunobu, and Inoue, Hiroyuki

Subjects
*SULFURIC acid, *STRUCTURAL analysis (Science), *X-ray diffraction, *EXTENDED X-ray absorption fine structure, *MOLECULAR dynamics, *CHEMICAL bonds, *TITANIUM, *MANGANESE
Abstract

Structural analyses have been performed for sulfuric acid (H2SO4) aqueous solutions containing Ti and/or Mn. These solutions are used as the positive electrolyte in the Ti–Mn redox flow (RF) battery, in which it had been found that adding Ti4+ in the positive electrolyte is very effective to reduce the MnO2 precipitation at a high state of charge. X-ray diffraction and x-ray absorption fine structure (XAFS) measurements were employed in order to obtain total correlation functions, T(r)’s, and coordination numbers around Mn and Ti in the solutions, respectively. The T(r)’s showed some peculiar peaks that were assigned to correspond to S—O, O—O, Mn—O, and Ti—O pairs in the solutions. The XAFS analysis demonstrated that both Mn and Ti have 6-coordinating oxygen atoms in the solutions. The classical molecular dynamics simulation was also carried out to obtain structural models of the solutions. By tuning the Born-Mayer type potential parameters, the T(r)’s calculated from the models showed good agreement with the experimental ones. Regarding the coordination number, the 6-coordinated Mn—O was reproduced successfully, while we need further investigation to find parameters that can reproduce the 6-coordinated Ti—O in the solutions. The simulation results also indicated the existence of Ti—SO4 bonds, which should promote the H+ dissociation from HSO4− and increase the H+ concentration in the solutions. This may be effective to suppress the MnO2 precipitation at a high state of charge in the RF battery. [ABSTRACT FROM AUTHOR]

Published
2018
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14. Time-Resolved Coherent Diffraction of Ultrafast Structural Dynamics in a Single Nanowire

Author

Newton, Marcus C., primary, Sao, Mayu, additional, Fujisawa, Yuta, additional, Onitsuka, Rena, additional, Kawaguchi, Tomoya, additional, Tokuda, Kazuya, additional, Sato, Takahiro, additional, Togashi, Tadashi, additional, Yabashi, Makina, additional, Ishikawa, Tetsuya, additional, Ichitsubo, Tetsu, additional, Matsubara, Eiichiro, additional, Tanaka, Yoshihito, additional, and Nishino, Yoshinori, additional

Published
2014
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15. What determines the critical size for phase separation in LiFePO4 in lithium ion batteries?

Author

Ichitsubo, Tetsu, Doi, Takayuki, Tokuda, Kazuya, Matsubara, Eiichiro, Kida, Tetsuya, Kawaguchi, Tomoya, Yagi, Shunsuke, Okada, Shigeto, Yamaki, Jun-ichi, Ichitsubo, Tetsu, Doi, Takayuki, Tokuda, Kazuya, Matsubara, Eiichiro, Kida, Tetsuya, Kawaguchi, Tomoya, Yagi, Shunsuke, Okada, Shigeto, and Yamaki, Jun-ichi

Abstract

LiFePO4 characteristically shows a plateau voltage due to a two-phase (LiFePO4/FePO4) separation during the charge/discharge process in Li ion batteries. In this study, we clearly show that monodispersed nano-sized (about 10 nm) LiFePO4 particles exhibit a complete single-phase reaction without showing any plateau voltage. Since the elastic strain due to lattice mismatch between LiFePO4 and FePO4 would be easily released near the surface, elastic effects are usually expected to weaken, but, in contrast to this expectation, phase separation does not occur experimentally in such small nanoparticles. Consideration on the basis of only static thermodynamics is insufficient to explain why such a single-phase reaction occurs in nano-sized particles. In contrast, the mechanism of the single-phase reaction can be naturally understood, when we consider a kinetics concept based on the preferred wavelength for stable growth of the spinodal wave under such an elastic constraint.

Published
2013

16. Elastically constrained phase-separation dynamics competing with the charge process in the LiFePO4/FePO4 system

Author

Ichitsubo, Tetsu, Tokuda, Kazuya, Yagi, Shunsuke, Kawamori, Makoto, Kawaguchi, Tomoya, Doi, Takayuki, Oishi, Masatsugu, Matsubara, Eiichiro, Ichitsubo, Tetsu, Tokuda, Kazuya, Yagi, Shunsuke, Kawamori, Makoto, Kawaguchi, Tomoya, Doi, Takayuki, Oishi, Masatsugu, and Matsubara, Eiichiro

Abstract

By using phase-field computer simulations, we have investigated the effects of the coherent strain due to the phase separation in the olivine-type LiFePO[4]. In this system, the coherent elastic-strain energy due to the lattice mismatch between LiFePO[4] and FePO[4] phases accompanied by insertion and extraction of Li ions is considered to play a crucial role in the phase separation kinetics during the charge/discharge process. The present phase-field micromechanics simulations reveal several significant features of the LiFePO[4]/FePO[4] system accompanying the coherent strain, such as the retardation of the phase separation, the charge rate dependence, the thermodynamic stability of coherent interfaces between dual phases, etc. Nucleation of the new phase is found to be fundamentally unlikely in terms of the elastic strain energy, except in the vicinity of the surface of the particles, and thus the phase separation would be dominated by the spinodal decomposition process. When the nucleus is present precedently, however, the phase separation can proceed in the mixture mode of the domino cascade and spinodal decomposition processes.

Published
2013

17. Time-resolved Bragg coherent X-ray diffraction revealing ultrafast lattice dynamics in nano-thickness crystal layer using X-ray free electron laser

Author

Tanaka, Yoshihito, Ito, Kiminori, Nakatani, Takashi, Onitsuka, Rena, Newton, Marcus, Sato, Takahiro, Togashi, Tadashi, Yabashi, Makina, Kawaguchi, Tomoya, Shimada, Koki, Tokuda, Kazuya, Takahashi, Isao, Ichitsubo, Tetsu, Matsubara, Eiichiro, Nishino, Yoshinori, Tanaka, Yoshihito, Ito, Kiminori, Nakatani, Takashi, Onitsuka, Rena, Newton, Marcus, Sato, Takahiro, Togashi, Tadashi, Yabashi, Makina, Kawaguchi, Tomoya, Shimada, Koki, Tokuda, Kazuya, Takahashi, Isao, Ichitsubo, Tetsu, Matsubara, Eiichiro, and Nishino, Yoshinori

Abstract

Ultrafast time-resolved Bragg coherent X-ray diffraction (CXD) has been performed to investigate lattice dynamics in a thin crystal layer with a nanoscale thickness by using a SASE (Self-Amplified Spontaneous Emission)-XFEL (X-ray Free Electron Laser) facility, SACLA. Single-shot Bragg coherent diffraction patterns of a 100 nm-thick silicon crystal were measured in the asymmetric configuration with a grazing exit using an area detector. The measured coherent diffraction patterns showed fringes extending in the surface normal direction. By using an optical femtosecond laser-pump and the XFEL-probe, a transient broadening of coherent diffraction pattern profile was observed at a delay time of around a few tens of picosecond, indicating transient crystal lattice fluctuation induced by the optical laser. A perspective application of the time-resolved Bragg CXD method to investigate small sized grains composing ceramic materials is discussed. (C)2013 The Ceramic Society of Japan. All rights reserved.

Published
2013

20. Time-resolved Bragg coherent X-ray diffraction revealing ultrafast lattice dynamics in nano-thickness crystal layer using X-ray free electron laser

Author

TANAKA, Yoshihito, primary, ITO, Kiminori, additional, NAKATANI, Takashi, additional, ONITSUKA, Rena, additional, NEWTON, Marcus, additional, SATO, Takahiro, additional, TOGASHI, Tadashi, additional, YABASHI, Makina, additional, KAWAGUCHI, Tomoya, additional, SHIMADA, Koki, additional, TOKUDA, Kazuya, additional, TAKAHASHI, Isao, additional, ICHITSUBO, Tetsu, additional, MATSUBARA, Eiichiro, additional, and NISHINO, Yoshinori, additional

Published
2013
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24. What determines the critical size for phase separation in LiFePO4 in lithium ion batteries?

Author

Ichitsubo, Tetsu, Doi, Takayuki, Tokuda, Kazuya, Matsubara, Eiichiro, Kida, Tetsuya, Kawaguchi, Tomoya, Yagi, Shunsuke, Okada, Shigeto, and Yamaki, Jun-ichi

Abstract

LiFePO4 characteristically shows a plateau voltage due to a two-phase (LiFePO4/FePO4) separation during the charge/discharge process in Li ion batteries. In this study, we clearly show that monodispersed nano-sized (about 10 nm) LiFePO4 particles exhibit a complete single-phase reaction without showing any plateau voltage. Since the elastic strain due to lattice mismatch between LiFePO4 and FePO4 would be easily released near the surface, elastic effects are usually expected to weaken, but, in contrast to this expectation, phase separation does not occur experimentally in such small nanoparticles. Consideration on the basis of only static thermodynamics is insufficient to explain why such a single-phase reaction occurs in nano-sized particles. In contrast, the mechanism of the single-phase reaction can be naturally understood, when we consider a kinetics concept based on the preferred wavelength for stable growth of the spinodal wave under such an elastic constraint. [ABSTRACT FROM AUTHOR]

Published
2013
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