Ion Diffusion in Solids Probed by Muon-Spin Spectroscopy

Abstract

Diffusion of Li+ ions in solids is a basic principle behind the operation of Li-ion batteries. Although a diffusion coefficient of Li + (D Li ) in solids is usually evaluated by 7 Li-NMR, difficulties arise for materials that contain magnetic ions. This is because the magnetic ions contribute additional spinlattice relaxation processes that are considerably larger than the 1/T 1 expected from only Li diffusion. As a result, it is very difficult to estimate correct D Li by Li-NMR, although D Li is one of the primary parameters that govern the charge and discharge rate of a Li-ion battery, particularly for the case of a future solid-state battery. We have, therefore, initiated to measure D Li in solids with muon-spin relaxation (µSR). Here, we summarize our µSR work on Li-diffusion and compare the µSR result with that obtained by QENS from the viewpoint of time window.

Na Diffusion in Quasi One-Dimensional Ion Conductor NaMn2O4 Observed by μ+SR

“…QENS is an excellent technique to determine both jump distance and jump frequency simultaneously. However, the measurable range of D is above 10 −9 cm 2 /s, which is 100 times higher than the typical D for battery materials at room temperature [8].…”

Li-Ion Dynamics in Li5+xLa3ZrxNb2−xO12

“…Furthermore, considering the limited time window of µ + SR, we have also measured QENS spec- tra for LLZONb, particularly at high temperatures. This is because µ + SR is too sensitive to detect D Li ranging above about 10 −8 cm 2 /s [7]. Here, we report the results obtained by both µ + SR and QENS measurements on LLZONb and extract the predominant parameter for determining σ Li .…”

“…However, considering the parameters to determine σ Li , we could line up the following two candidates; namely, a diffusion coefficient of Li + (D Li ) and the number density of mobile Li + (n Li ). Unfortunately, it is difficult to measure n Li directly, while there are three microscopic techniques to measure intrinsic D Li in solids [5][6][7], that is, a Li-NMR, quasielastic neutron scattering (QENS), and positive muon-spin relaxation (µ + SR) technique.…”

Emergent magnetism from lithium freezing in lithium-doped boron nitride

“…other Li diffusion constants from μSR experiments [26,32,33]. Given that our system is dilute, there are a large number of vacant sites that the Li can jump to and since the structure is layered, the Li atoms can move freely throughout the structure and so the value of D Li may be reasonable.…”