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arXiv · 2507.05626

Uncovering coupled ionic-polaronic dynamics and interfacial enhancement in Li$_x$FePO$_4$

Fengyu Xie·Yuxiang Gao·Ruoyu Wang·Zhicheng Zhong
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Abstract

Understanding and controlling coupled ionic-polaronic dynamics is crucial for optimizing electrochemical performance in battery materials. However, studying such coupled dynamics remains challenging due to the intricate interplay between Li-ion configurations, polaron charge ordering, and lattice vibrations. Here, we develop a fine-tuned machine-learned force field (MLFF) for Li$_x$FePO$_4$ that captures coupled ion-polaron behavior. Our simulations reveal picosecond-scale polaron flips occurring orders of magnitude faster than Li-ion migration, featuring strong correlation to Li configurations. Notably, polaron charge fluctuations are further enhanced at Li-rich/Li-poor phase boundaries, suggesting a potential interfacial electronic conduction mechanism. These results demonstrate the capability of fine-tuned MLFFs to resolve complex coupled transport and provide insight into emergent ionic-polaronic dynamics in multivalent battery cathodes.

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Fengyu Xie, Yuxiang Gao, Ruoyu Wang, Zhicheng Zhong. 2025-07-08. Uncovering coupled ionic-polaronic dynamics and interfacial enhancement in Li$_x$FePO$_4$. https://arxiv.org/abs/2507.05626

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