⁷Li NMR and Two-Dimensional Exchange Study of Lithium Dynamics in Monoclinic Li₃V₂(PO₄)₃

Abstract

High-resolution solid-state (7)Li NMR was used to characterize the structure and dynamics of lithium ion transport in monoclinic Li(3)V(2)(PO(4))(3). Under fast magic-angle spinning (MAS) conditions (25 kHz), three resonances are clearly resolved and assigned to the three unique crystallographic sites. This assignment is based on the Fermi-contact delocalization interaction between the unpaired d-electrons at the vanadium centers and the lithium ions. One-dimensional variable-temperature NMR and two-dimensional exchange spectroscopy (EXSY) are used to probe Li mobility between the three sites. Very fast exchange, on the microsecond time scale, was observed for the Li hopping processes. Activation energies are determined and correlated to structural properties including interatomic Li distances and Li-O bottleneck sizes.

From Ultraslow to Fast Lithium Diffusion in the 2D Ion ConductorLi0.7TiS2Probed Directly by Stimulated-Echo NMR and Nuclear Magnetic Relaxation

“…This Letter emphasizes the direct, i.e., model-independent, measurement of ultraslow Li jumps in TiS 2 with rates from the kHz to the sub-Hz range by 7 Li spin-alignment echo (SAE) NMR. The method was originally developed for deuterons by Spiess [2] and, quite recently, successfully applied also to spin-3=2 nuclei, like 9 Be [3] and 7 Li [4]. Recording two-time 7 Li SAE singleparticle correlation functions enables direct access to Li jump rates.…”

“…To our knowledge, only few Li 2D NMR experiments have been performed until now; see, e.g., Refs. [5][6][7].Here, polycrystalline layer-structured Li x TiS 2 with x 0:7 was chosen as a unique model substance for a comprehensive investigation of 2D Li diffusion. For the first time, jump rates from 7 Li SAE NMR with values down to the sub-Hz range were systematically compared to those obtained from classical 7 Li NMR relaxation probing Li diffusion on a much shorter time scale with jump rates up to the GHz range.…”

“…The method is applicable at relatively low temperatures, so that it is expected to become one of the leading techniques for the study of Li dynamics in numerous, possibly heat-sensitive Li conductors. Compared to two-dimensional (2D) Li exchange NMR [5], which is also capable to measure very slow Li jumps directly in the present sense, 7 Li SAE NMR is much less time consuming and applicable to a much broader class of crystalline and even amorphous materials. Furthermore, a much larger dynamic range can be investigated which is about four decades in the present study.…”

Studying Li Dynamics in a Gas-Phase Synthesized Amorphous Oxide by NMR and Impedance Spectroscopy

“…In particular, the investigation of Li dynamics over a wide length scale turns out to be highly important to understand the underlying structure-property relationships governing ion transport in materials being relevant for battery applications [5][6][7][8][9][10][11][12][13][14][15]. For instance, fast ion conductors are needed to develop powerful all-solid-state lithium-ion batteries which are regarded to play a key role in the development of new energy storage systems [16][17][18].…”

New prospects in studying Li diffusion—two-time stimulated echo NMR of spin-3/2 nuclei

“…Furthermore, stimulated echo NMR allows the measurement of extremely slow Li jumps with rates in the kHz to sub-Hz range. Recently, also 2D exchange 3 6 Li and 7 Li NMR experiments were used for the study of Li jump rates in the kHz range very successfully [10][11][12]. To our knowledge, so far only these few magic angle spinning (MAS) 2D exchange NMR experiments have been carried out to detect Li jumps between crystallographic distinct sites.…”