電池材料の「協奏的なイオン輸送」を可視化する新理論を開発～渋滞学がイオンの集団運動を読み解き、高速イオン伝導の物理を解明～

2025-12-17 東京大学

二次元超イオン伝導体Na₂Ni₂TeO₆中の協奏的な輸送が
有向グラフ解析により可視化される様子および計算されるイオン伝導度

＜関連情報＞

• https://www.t.u-tokyo.ac.jp/press/pr2025-12-17-002
• https://www.t.u-tokyo.ac.jp/hubfs/press-release/2025/1217/002/text.pdf
• https://pubs.acs.org/doi/10.1021/acs.chemmater.5c02374

有向グラフによる超イオン伝導体の協調イオン移動の可視化 Visualizing Concerted Ion Migration of Superionic Conductors via Directed Graphs

Ryuhei SatoYasunobu AndoKartik Sau,and Yasushi Shibuta
Chemistry of Materials  Published: December 12, 2025
DOI:https://doi.org/10.1021/acs.chemmater.5c02374

Abstract

A directed-graph model is proposed to describe the concerted ion migration in superionic conductors. Here, each ion hopping during the molecular dynamics simulation is represented as a displacement vector. One hopping event is then temporally and spatially connected to another based on a cutoff distance determined from the short-range part of the van Hove correlation function (i.e., closer than the first peak of the pair distribution function), thereby reconstructing the concerted ion migration. This enables the quantitative visualization of concerted migration within short time intervals. The parameters of this model are derived from physically meaningful quantities such as jump distances, diffusion coefficients, and pair distribution functions, reducing the reliance on arbitrary hyperparameters. We applied the model to Li₁₀GeP₂S₁₂, Na₂Ni₂TeO₆, and AgI, demonstrating its general applicability and robustness. The model quantitatively bridges microscopic ion trajectories with macroscopic ionic conductivity. It accurately reproduces the ion conductivity obtained via the Green–Kubo formalism with ion–ion correlations, corresponding to conductivities measured by electrochemical methods such as impedance spectroscopy. This consistency validates the concerted migration picture from our directed-graph model, where more than five ions are frequently involved in each concerted migration event. Our analysis further reveals that enhanced conductivity is linked to a local “correlation distance” between hopping ions. This suggests that controlling local interactions such as ion-lattice coupling offers a pathway to optimize the concerted ion migration in superionic conductors.