Prof. Dr. Hirofumi Yoshikawa
Kwansei Gakuin University
Prof. Dr. Hirofumi Yoshikawa
About the Speaker
Prof. Dr. Hirofumi Yoshikawa focuses on the development of advanced materials for next-generation energy storage systems, particularly rechargeable batteries and capacitors. His research centers on redox-active molecular materials, especially polynuclear metal complex clusters (“molecular clusters”), which can undergo multi-electron redox reactions and serve as high-performance cathode materials in lithium batteries.
By integrating these molecular clusters with nanocarbon materials—such as single-walled carbon nanotubes, graphene, and mesoporous carbon—his group develops nano-hybrid electrode materials that significantly improve battery performance. These hybrids combine the redox activity of molecular clusters with the electrical double-layer capacitance of nanocarbons, resulting in higher capacity, faster charge/discharge rates, and improved power density compared with conventional cathode materials.
Overall, Prof. Yoshikawa’s work aims to advance both the fundamental understanding and practical development of innovative energy storage materials to support future sustainable energy systems.
Learn more about Prof. Dr. Prof. Dr. Hirofumi Yoshikawa.External link
Abstract
Mulrti-valent ion batteries using organic framework structure materials
Calcium-ion batteries (CIBs) are promising energy storage systems because of their low cost and high theoretical volumetric energy density. However, calciumion (Ca2+), a divalent cation with a larger ionic radius than lithium ion, forms strong electrostatic interactions with the divalent O2? anion in conventional metal-oxide-based cathode active materials, resulting incapacities less than55%of the theoretical values and poor rate performance. In this study, Cu3(HHTP)2 (HHTP: 2,3,6,7,10,11- hexahydroxytriphenylene), a two-dimensional metal-organic framework with monovalentO?anions included in its crystal structure, is used as a cathode active material for CIBs, and its performance, as well as its calciation and de-calciation mechanisms, is investigated. Cu3(HHTP)2 has a high initial capacity equal to 86% of the theoretical value and excellent rate performance owing to sufficient redox reaction and smooth calciation, respectively. However, it exhibits poor cycle performance because of insufficient de-calciation during charging, which results from electrostatic interactions between intercalatedCa2+ ionswithO? anions in the narrower interlayer spacingofCu3(HHTP)2 after the first discharge. These findings provide valuable insights for improving the performance of cathode active materials for CIBs.
References:
MK. Wakamatsu, S. Ohkata, M. Kajiwara, N. Tanifuji, H. Yoshikawa, T. Shimizu
ACS Electrochemistry, (2026) 2, 3, 596-603 (DOI: 10.1021/acselectrochem.5c00241) (Selected as Supplementary Cover)