HOME > Profile > IIMURA, Reona
- Address
- 305-0044 1-1 Namiki Tsukuba Ibaraki JAPAN [Access]
Research
- Keywords
多価金属電池、材料化学、結晶構造解析
PublicationsNIMS affiliated publications since 2004.
Society memberships
電気化学会, 日本セラミックス協会, 軽金属学会
Research Center for Energy and Environmental Materials (GREEN)
Title
Design of Positive Electrode Materials for Rechargeable Multivalent Batteries
Keywords
Multivalent Batteries, Inorganic Materials Synthesis, Crystal Structure Analysis, Nanomaterials
Overview
In recent years, growing geopolitical instability and resource constraints have driven increasing demand for next-generation rechargeable batteries that reduce dependence on critical metals and utilize earth-abundant, readily available elements. Among the promising candidates are rechargeable multivalent metal batteries employing magnesium (Mg) or calcium (Ca) metal anodes, owing to their natural abundance and low redox potentials. These battery systems offer the potential to achieve both high safety and high energy density through appropriate materials and cell design. However, research and development remain largely focused on individual battery components, and significant challenges must be overcome before practical battery cells can be realized.A major challenge for positive electrode materials is the strong electrostatic interaction between multivalent ions and anions in the crystal lattice, which hinders ion migration within the solid. Therefore, enabling fast and reversible ion transport while maintaining structural stability is essential.To address these challenges, we focus on the design and development of positive electrode materials that enable fast and reversible insertion and extraction of multivalent ions, with particular emphasis on crystal structure stability, solid-state ion transport, and material morphology control. By combining inorganic materials synthesis with advanced structural characterization using synchrotron radiation techniques and computational approaches, we aim to elucidate the relationships between crystal structures and electrochemical properties, ultimately contributing to the development of high-performance rechargeable multivalent metal batteries.
Novelty and originality
・Achieved room-temperature operation of multivalent metal batteries through the ultrasmall nanosizing of oxide positive electrode materials.
・Developed oxide frameworks enabling reversible insertion and extraction of multivalent ions.
・Revealed through detailed crystal structure analysis that the combination of structural robustness and flexibility of ion diffusion pathways is a key factor governing multivalent ion diffusion.
Details
Tunnel-structured MnO2 has long been considered a promising positive electrode material for rechargeable multivalent metal batteries, as suggested by computational studies and electrochemical tests at elevated temperatures. However, sluggish solid-state diffusion of multivalent ions has limited its electrochemical performance at room temperature. To overcome this limitation, we focused on reducing ion diffusion distances through extreme nanosizing of MnO2 particles. Using a newly developed alcohol-based solution method, we successfully synthesized crystalline MnO2 nanoparticles with sizes in the single-digit nanometer range, which had previously been difficult to achieve.The resulting ultrasmall MnO2 nanoparticles enabled rechargeable multivalent metal battery operation at room temperature, delivering high capacity and rate capability. Furthermore, detailed structural analyses revealed that approximately 0.3 Ca ions per Mn atom can be reversibly inserted and extracted, demonstrating the potential of this material as a positive electrode for rechargeable calcium metal batteries.Beyond their application as positive electrode materials for multivalent metal batteries, the developed ultrasmall MnO2 nanoparticles also hold promise for applications in catalysis and sensing, offering potential benefits across a wide range of fields.
To achieve reversible insertion and extraction of larger amounts of multivalent ions, we focused on h-MoO3, which possesses a geometrically stable hexagonal tunnel structure. Our material design strategy aimed to enable reversible charge–discharge reactions at room temperature by reducing solid-state ion diffusion limitations through nanosizing while preserving the stability of the crystal framework. Electrochemical evaluations using the synthesized h-MoO3 as a positive electrode material demonstrated reversible insertion and extraction of both Mg ion and Ca ion at room temperature. Notably, the crystal lattice exhibited an exceptionally small volume change of less than 2% during charge–discharge reactions, indicating that the reactions proceed while maintaining the integrity of the crystal framework. Furthermore, by combining detailed crystal structure analysis with computational approaches, we revealed that local Mo–O bonds undergo reversible expansion and contraction in response to multivalent ion insertion and extraction while preserving the robust crystal framework. These findings demonstrate that the combination of structural robustness and local bond flexibility is a key factor enabling reversible multivalent ion insertion and extraction, opening new possibilities for the design of positive electrode materials for rechargeable multivalent metal batteries.
Summary
With a focus on crystal structure stability, solid-state ion transport, and material morphology control, we aim to develop high-performance positive electrode materials for rechargeable multivalent metal batteries by integrating inorganic materials synthesis, advanced crystal structure analysis, and computational approaches. Furthermore, through materials synthesis-driven research, we seek to develop novel materials with broad applicability across diverse material systems and advance the fundamental materials science underlying their design.
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