Affiliation Department etc.

Department of Life Science and Applied Chemistry
Department of Life Science and Applied Chemistry
Center for Innovative Young Researchers




  • Molecular Dynamics Simulation of Li-Ion Conduction at Grain Boundaries in NASICON-Type LiZr2(PO4)3 Solid Electrolytes

    Koki Nakano, Naoto Tanibata, Hayami Takeda, Ryo Kobayashi, Masanobu Nakayama, Naoki Watanabe

    The Journal of Physical Chemistry C ( American Chemical Society (ACS) )  125 ( 43 ) 23604 - 23612   2021.11  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • Exploring the diffusion mechanism of Li ions in different modulated arrangements of La(1-X)/3LixNbO3 with fitted force fields obtained via a metaheuristic algorithm

    Zijian Yang, Robyn E. Ward, Naoto Tanibata, Hayami Takeda, Masanobu Nakayama, Ryo Kobayashi

    SOLID STATE IONICS ( ELSEVIER )  366   2021.08

    Research paper (scientific journal)   Multiple Authorship

    As a potential solid-state electrolyte material, Li-containing A-site deficient perovskite oxides have attracted the attention of researchers because of their high Li-ion conductivity and the relationship between Li-ion conduction and structural characteristics, which has been intensively investigated. We have recently confirmed a quasiperiodic ordered arrangement of La and vacancies (Vac) at the perovskite A-sites of La(1-X)/3LixNbO3 (LLNO) using a combination of density functional theory (DFT), Monte Carlo simulations, and electron diffraction. Interestingly, two types of modulated arrangements, namely closed and striped structures, coexist in the La-rich layer, which affect Li-ion migration. In this study, DFT-derived force-field molecular dynamics (FFMD) simulations were performed to investigate the effect of a modulated structure on the migration behavior of Li ions in LLNO compounds. The results indicate that the type of modulated arrangements of La/Vac has a significant influence on the migration of Li ions. Moreover, the estimated diffusion coefficients of the modulated structures are higher by a factor of 10 than those of La/Vac disordered models at 800 K. The migration energy in the ab plane appeared to be much lower than along the c-axis, controlling the modulated arrangement of LLNO is beneficial to eliminate La-ion blockage during long-distance migration. Accordingly, the present study reveals that the controlling cation/Vac arrangement at perovskite A-sites is crucial for achieving high Li-ion conductivity. At the same time, the research scheme of this work is also applicable to other solid electrolyte materials, which provides research guidance for high-throughput material retrieval.

  • First-principles study of the morphology and surface structure of LaCoO3 and La0.5Sr0.5Fe0.5Co0.5O3 perovskites as air electrodes for solid oxide fuel cells

    Masanobu Nakayama, Katsuya Nishii, Kentaro Watanabe, Naoto Tanibata, Hayami Takeda, Takanori Itoh, Toru Asaka

    Science and Technology of Advanced Materials   1 ( 1 ) 24 - 33   2021.03  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • Efficient Experimental Search for Discovering a Fast Li-Ion Conductor from a Perovskite-Type LixLa(1-x)/3NbO3 (LLNO) Solid-State Electrolyte Using Bayesian Optimization

    Zijian Yang, Shinya Suzuki, Naoto Tanibata, Hayami Takeda, Masanobu Nakayama, Masayuki Karasuyama, Ichiro Takeuchi

    JOURNAL OF PHYSICAL CHEMISTRY C ( AMER CHEMICAL SOC )  125 ( 1 ) 152 - 160   2021.01

    Research paper (scientific journal)   Multiple Authorship

    LixLa(l -x)/3NbO3 (LLNO) is an A-site-deficient perovskite material that has a larger unit cell volume, a lower La3+ concentration, and a higher intrinsic vacancy concentration than (LixLa(2-x)/3TiO3), which is known to be one of the fastest Li-ion conductive oxides. These advantages make LLNO a potential oxide-based solid electrolyte candidate for allsolid-state Li-ion batteries. The A-site and B-site elements in this perovskite-type material can be substituted by ions with various charges and radii in a wide range of ways to form complicated solid solutions; hence, this type of material can be adapted to a variety of application requirements. Doping with monovalent or divalent metal compounds is a promising method for improving the ionic conductance of this perovskite-type material. In this study, the (LiyLa(1-y/3)(1-x)Sr0.5xNbO3 (0 <= 0.5 x <= 0.15, 0 <= y <= 0.3) composition formed by co-doping with Li2CO3 and SrCO3 was optimized using an exhaustive experimental approach. Sixty-four samples with different compositions were structurally analyzed, and their electrochemical performance was experimentally characterized, which revealed that the co-doped samples have higher ionic conductivities and superior sintered morphologies compared to those prepared by single doping. Because Li+ and Sr2+ doping improves the ionic conductivity for different reasons, and many factors, such as higher carrier concentrations, enhancements through sintering, and changes in the microstructure, play important roles, it is difficult or inefficient to determine the best composition using only traditional trial-and-error or intuitive searching. Instead, as a proof-of-concept study, we show that the Bayesian optimization (BO) method efficiently searches for the best composition and that material retrieval during experimental exploration can benefit from BO because it significantly reduces the high workload associated with the trial-and-error approach employed by the materials industry.

  • Bayesian-optimization-guided experimental search of NASICON-type solid electrolytes for all-solid-state Li-ion batteries

    Maho Harada, Hayami Takeda, Shinya Suzuki, Koki Nakano, Naoto Tanibata, Masanobu Nakayama, Masayuki Karasuyama, Ichiro Takeuchi

    JOURNAL OF MATERIALS CHEMISTRY A ( ROYAL SOC CHEMISTRY )  8 ( 30 ) 15103 - 15109   2020.08  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    Divalent- or trivalent-metal-oxide-doped NASICON-type LiZr2(PO4)(3)(LZP) is an attractive oxide-based solid electrolyte for all-solid-state Li-ion batteries owing to its high Li-ion conductivity and stable charge-discharge cycling. Using an extensive experimental approach, the composition of CaO- and Y2O3-co-doped Li-rich NASICON-type LZP of the composition Li(1+x+2y)Z(r2-x-y)Y(x)Ca(y)(PO4)(3)(0 <= x <= 0.376, 0 <= y <= 0.376) was optimized. A number of 49 compositions were synthesized and their crystal structures, relative density of the sintered material, and Li-ion conductivity characterized. The co-doped compositions had a higher Li-ion conductivity than those doped with CaO or Y(2)O(3)alone. Furthermore, diffraction studies revealed that two phases and an impurity phase existed depending on the composition. Adding CaO significantly changed the relative density of the sintered material. Thus, to identify compositional dependencies among the Li-ion conductivity, phase stability, and relative density was complicated, and intuitively searching for the best composition was difficult. As a proof-of-concept, the collected data were used to demonstrate that the Bayesian optimization (BO) significantly improved the experimental search for the best oxide-based electrolyte composition. Multi-objective BO (MOBO), which considers more than two target performances, was also carried out. It was validated that the BO-guided experimental search determined more rapidly the best composition compared to conventional trial-and-error approaches employed in the materials industry.

  • Arrangement in La1/3NbO3 Obtained by First-Principles Density Functional Theory with Cluster Expansion and Monte Carlo Simulation

    Zijian Yang, Robyn E. Ward, Naoto Tanibata, Hayami Takeda, Masanobu Nakayama, Toru Asaka

    JOURNAL OF PHYSICAL CHEMISTRY C ( AMER CHEMICAL SOC )  124 ( 18 ) 9746 - 9754   2020.05  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    LixLa(1-x)/3NbO3 is an A-site-deficient perovskite material that exhibits structure-dependent ionic conductivity. La1/3NbO3 has a larger unit cell volume, lower concentration of La3+ ions, and higher concentration of intrinsic vacancies than La2/3TiO3. As such, it should exhibit higher Li ion conductivity and, therefore, be a good candidate for all ceramic Li secondary batteries or fast Li ion transport solid-state electrolyte batteries. However, experimental observations show otherwise. Information on the local atomic arrangements would facilitate the analysis of the gap between the theoretical and experimental results. Ab initio density functional theory calculations are useful for calculating the atomic arrangements and energies. However, because of cell size limitations, long-range ordering in La/Li/vacancy arrangements cannot be observed using ab initio calculations. In this study, cluster expansion and Monte Carlo simulations were utilized to bridge this gap. The computational results reproduce the stacking of alternate La-rich and La-poor layers along the c-axis, consistent with the experimental data. In addition, two possible modulated structures for the La-rich layers were discovered. These should help explain the lower-than-expected ionic conductivity and the possible Li ion migration pathways in the material. Based on the presented Monte Carlo simulations, we conclude that the two types of low-energy structures, the closed and striped arrangements, may coexist in the real system. The modulated structures in experimental studies are likely to be numberless nanodomains composed of these two arrangements. If the majority of the structure shows a closed arrangement at room temperature, most of the Li ions will be trapped at the center of the periodic units in the closed arrangement. This could explain the lower-than-expected Li ion conductivity in LixLa(1-x)/3NbO3.

  • Exhaustive and informatics-aided search for fast Li-ion conductor with NASICON-type structure using material simulation and Bayesian optimization

    Koki Nakano, Yusuke Noda, Naoto Tanibata, Hayami Takeda, Masanobu Nakayama, Ryo Kobayashi, Ichiro Takeuchi

    APL MATERIALS ( AMER INST PHYSICS )  8 ( 4 )   2020.04  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    Currently, NASICON-type LiZr2(PO4)(3) (LZP)-related materials are attracting attention as solid electrolytes. There are experimental reports that Li-ion conductivity can be improved by doping a small amount of Ca or Y into stoichiometric LZP. In previous studies, doping with only one element having a narrow search space has been attempted, and thus, further improvement of the Li-ion conductivity is conceivable by using multi-element doping. When multi-element doping is attempted, because the search space becomes enormous, it is necessary to evaluate the Li-ion conductivity using a low-cost method. Here, force-field molecular dynamics using a bond valence force field (BVFF) approach was performed to evaluate the Li-ion conductivity. We confirmed that the Li-ion conductivity of stoichiometric LZP derived from BVFF (6.2 x 10(-6) S/cm) has good agreement with the first principle calculation result (5.0 x 10(-6) S/cm). Our results suggest that the Li-ion conductivity can be further improved by simultaneously doping LZP with Ca and Y [6.1 x 10(-5) S/cm, Li35/32Ca1/32Y1/32Zr31/16(PO4)(3)]. In addition, Bayesian optimization, which is an informatics approach, was performed using exhaustively computed conduction property datasets in order to validate efficient materials search. The averages for Bayesian optimization over 1000 trials show that the optimal composition can be found about seven times faster than by random search.

  • First-Principles Density Functional Theory Calculations for Formic Acid Adsorption onto Hydro-Garnet Compounds

    Masanobu Nakayama, Kunihiro Ishida, Kentaro Watanabe, Naoto Tanibata, Hayami Takeda, Hirotaka Maeda, Toshihiro Kasuga

    ACS OMEGA ( AMER CHEMICAL SOC )  5 ( 8 ) 4083 - 4089   2020.03  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    Efficient and large-scale removal of humic acid (HA) from aqueous environments is required since HA causes human health and esthetic issues. Hydrogarnet compounds, Ca3Al2(SiO4)(3-x)(OH)(4x), have recently been suggested as HA adsorbents not only due to their superior adsorption behaviors but also because they are ubiquitous element-derived compounds. In this study, the adsorption behavior of formic acid to hydro-garnets was investigated by means of first-principles density functional theory (DFT) computations. Formic acid was chosen owing to its reasonable computational cost and inclusion of carboxylic acid as HA. Comparisons of adsorption energies for formic acid among various compounds (including platinum and kaolinite) indicate that hydro-garnet compounds are promising due to their lower more stable) adsorption energies. Also, the optimization of composition x enables selective adsorption of formic acid against solvent water molecules. Relationships between surface electronic/atomistic structures and adsorption properties are discussed.

  • Asymmetry in the Solvation–Desolvation Resistance for Li Metal Batteries

    Naoto Tanibata, Riku Morimoto, Kei Nishikawa, Hayami Takeda, Masanobu Nakayama

    Analytical Chemistry   92 ( 5 ) 3499 - 3502   2020.03  [Refereed]

    Research paper (scientific journal)   Multiple Authorship


  • Novel Mg-ion conductive oxide of mu-cordierite Mg0.6Al1.2Si1.8O6

    Hayami Takeda, Koki Nakano, Naoto Tanibata, Masanobu Nakayama

    SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS ( TAYLOR & FRANCIS LTD )  21 ( 1 ) 131 - 138   2020.01  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    Solid electrolytes with high Mg-ion conductivity are required to develop solid-state Mg-ion batteries. The migration energies of the Mg2+ ions of 5,576 Mg compounds tabulated from the inorganic crystal structure database (ICSD) were evaluated via high-throughput calculations. Among the computational results, we focused on the Mg2+ ion diffusion in Mg0.6Al1.2 Si1.8O6, as this material showed a relatively low migration energy for Mg2+ and was composed solely of ubiquitous elements. Furthermore, first-principles molecular dynamics calculations confirmed a single-phase Mg2+ ion conductor. The bulk material with a single Mg0.6Al1.2Si1.8O6 phase was successfully prepared using the sol-gel method. The relative density of the sample was 81%. AC impedance measurements indicated an electrical conductivity of 1.6 x 10(-6) Scm(-1) at 500 degrees C. The activation energy was 1.32 eV, which is comparable to that of monoclinic-type Mg0.5Zr2(PO4)(3).

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