Yuki Umemura
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Research Subjects
Yuki Umemura has a total of 10 co-authors. Here are the top co-authors by number of shared publications:
Hikari Sakaebe
National Institute of Advanced Industrial Science and Technology (AIST)
1 shared publication- Hikari Sakaebe
National Institute of Advanced Industrial Science and Technology (AIST)
1 shared publication Hisao Kiuchi
Office of Society-Academia Collaboration for Innovation, Kyoto University
1 shared publication- Jun Haruyama
Pioneering Research Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
1 shared publication - Minoru Otani
Center for Computational Sciences, University of Tsukuba
1 shared publication Misaki Katayama
SR Center, Ritsumeikan University
1 shared publication
Latest Publications
- Open Access
- 20 October 2022
- Published by The Electrochemical Society of Japan in Electrochemistry
- Vol. 90 (10) , 107002
Theoretical Consideration of Side Reactions between the VS4 Electrode and Carbonate Solvents in Lithium–metal Polysulfide Batteries
The lithium/vanadium tetra sulfide (Li|VS4) battery can be considered a promising next-generation battery because of its high theoretical energy density, and it is expected to overcome the problems inherent in Li-S batteries. However, the charge/discharge cycle degradation of the Li|VS4 battery strongly depends on the choice of the organic solvent. We investigated the equilibrium potentials of the decomposition reactions involving the VS4 electrode and organic solvent molecules using the density functional and classical solution theories. We first modelled the decomposition reactions between VS4 and different organic solvent molecules, such as ethylene, dimethyl, and propylene carbonates (EC, DMC, and PC). Next, we calculated the change in the Gibbs free energy of the decomposition reaction by assuming a thermodynamic cycle and estimated the equilibrium potential vs. Li/Li+. From the equilibrium potential, the overpotential of the DMC against the potential plateau of the Li|VS4 battery is negative and shows the lowest value in the considered solvents. This result suggests that the battery cycle with DMC deteriorates more quickly than that with EC and PC. This suggestion explains the experimental tendency of battery cycle degradation and will be a useful guide for improving the electrochemical performance of Li|VS4 batteries.
- 20 October 2022
- Published by The Electrochemical Society of Japan in Electrochemistry
- Vol. 90 (10) , 107002
Open AccessTheoretical Consideration of Side Reactions between the VS4 Electrode and Carbonate Solvents in Lithium–metal Polysulfide Batteries
The lithium/vanadium tetra sulfide (Li|VS4) battery can be considered a promising next-generation battery because of its high theoretical energy density, and it is expected to overcome the problems inherent in Li-S batteries. However, the charge/discharge cycle degradation of the Li|VS4 battery strongly depends on the choice of the organic solvent. We investigated the equilibrium potentials of the decomposition reactions involving the VS4 electrode and organic solvent molecules using the density functional and classical solution theories. We first modelled the decomposition reactions between VS4 and different organic solvent molecules, such as ethylene, dimethyl, and propylene carbonates (EC, DMC, and PC). Next, we calculated the change in the Gibbs free energy of the decomposition reaction by assuming a thermodynamic cycle and estimated the equilibrium potential vs. Li/Li+. From the equilibrium potential, the overpotential of the DMC against the potential plateau of the Li|VS4 battery is negative and shows the lowest value in the considered solvents. This result suggests that the battery cycle with DMC deteriorates more quickly than that with EC and PC. This suggestion explains the experimental tendency of battery cycle degradation and will be a useful guide for improving the electrochemical performance of Li|VS4 batteries.
- Open Access
- 5 May 2021
- Published by The Electrochemical Society of Japan in Electrochemistry
- Vol. 89 (3) , 273-278
Improvement of Cycle Capability of VS4 by Addition of Phosphorus Element
Vanadium tetrasulfide (VS4) have been attracting attention as the promising positive electrode material for next generation batteries because of its high theoretical capacity (1196 mAh g−1). In this study, a typical element (i.e., Phosphorus) was introduced into VS4 for an attempt to improve the electrochemical cycle performance of VS4. The prepared PxVSy showed significant increase in cycle capability; e.g., ca. 70 % after 50 cycles for P0.4VS5.0 sample cell, being much higher than that of pristine VS4 cell (ca. 10 %). The PDF (pair distribution function) analyses indicated that the structural reversibility of VS4 for Li insertion/extraction reactions was improved by the phosphorus addition.
- 5 May 2021
- Published by The Electrochemical Society of Japan in Electrochemistry
- Vol. 89 (3) , 273-278
Open AccessImprovement of Cycle Capability of VS4 by Addition of Phosphorus Element
Vanadium tetrasulfide (VS4) have been attracting attention as the promising positive electrode material for next generation batteries because of its high theoretical capacity (1196 mAh g−1). In this study, a typical element (i.e., Phosphorus) was introduced into VS4 for an attempt to improve the electrochemical cycle performance of VS4. The prepared PxVSy showed significant increase in cycle capability; e.g., ca. 70 % after 50 cycles for P0.4VS5.0 sample cell, being much higher than that of pristine VS4 cell (ca. 10 %). The PDF (pair distribution function) analyses indicated that the structural reversibility of VS4 for Li insertion/extraction reactions was improved by the phosphorus addition.