Student Seminar: Muon Spin Spectroscopy: A local probe of Ion Transport in Battery Materials

Ion transport in solids governs the performance of electrochemical energy storage systems. High ionic conductivity is essential for efficient batteries, and this macroscopic property arises from ionic diffusion at the atomic scale. Diffusion kinetics play a critical role in determining battery performance, as ion transport often acts as the rate-limiting step, directly influencing fast-charging capability and evolving during operation. Diffusion coefficients can be measured across different length scales using electrochemical and spectroscopic techniques; however, microscopic insight into ion dynamics is essential for a fundamental understanding and for tailoring material properties. Therefore, understanding ionic diffusion mechanisms and their relationship with crystal structure is critical for the rational design of next-generation energy materials.

In this talk, I will introduce muon spin relaxation (µSR) spectroscopy and discuss its usefulness in investigating ionic diffusion mechanisms at the atomic scale. The technique is sensitive to timescales of 10⁻⁵ to 10⁻⁸ s, enabling the study of both short-range and long-range ion motion. Compared to electrochemical impedance spectroscopy (EIS), which probes macroscopic diffusion including contributions from grain boundaries, interfaces, and defects, µSR provides direct microscopic insight into intrinsic ion dynamics. Furthermore, unlike Nuclear Magnetic Resonance (NMR), where fast relaxation in paramagnetic materials limits the ability to probe local ion motion, µSR remains effective, making it a powerful tool for studying ion diffusion in complex battery materials.

1. McClelland, I.; Johnston, B.; Baker, P. J.; Amores, M.; Cussen, E. J.; Corr, S. A. Muon Spectroscopy for Investigating Diffusion in Energy Storage Materials. Annu. Rev. Mater. Res. 2020, 50, 371–393.

2. Hillier, A. D.; Blundell, S. J.; McKenzie, I.; Umegaki, I.; Shu, L.; Wright, J. A.; Prokscha, T.; Bert,F.;Shimomura,K.;Berlie,A.;Alberto,H.;Watanabe,I.MuonSpinSpectroscopy. Nat. Rev. Methods Primers 2022, 2, 4.

3. Sugiyama, J.; Nozaki, H.; Harada, M.; Kamazawa, K.; Ofer, O.; Månsson, M.; Brewer, J. H.; Ansaldo, E.J.; Chow, K.H.; Kobayashi, G.Kanno, R. Magnetic and Diffusive Nature of LiFePO₄ Investigated by Muon Spin Rotation and Relaxation. Phys. Rev. B 2011, 84, 054430.