Proceedings of MATSUS Fall 2023 Conference (MATSUSFall23)
DOI: https://doi.org/10.29363/nanoge.matsus.2023.150
Publication date: 18th July 2023
Operando measurements are a powerful approach to understanding the performance and degradation of batteries. Nuclear magnetic resonance (NMR) spectroscopy is well-suited to such measurements due to its non-invasive, non-destructive nature and its sensitivity to both structure and dynamics. However, it does not come without challenges. Among them are technical aspects such as achieving realistic battery cycling performance with a minimum amount of metal in the operando cell, as well as reducing the interference between the battery and NMR electrical circuits. Moreover, the resolution of operando NMR spectra is much lower than in conventional solid-state NMR due to the absence of magic-angle spinning and the signal overlap from different cell components.
In this contribution, we demonstrate how the above challenges can be addressed and that operando NMR can provide information that may be difficult to obtain with other analytical techniques. We will focus on Li-ion batteries, presenting 7Li operando NMR data obtained on NMC811/graphite and LNO/graphite cells. Two aspects will be discussed in detail: Unwanted Li metal plating on graphite and the changes of structure and Li dynamics in the cathode materials.
Li metal deposition on graphite is an unwanted process which does not only accelerate capacity fade, but also poses a serious safety hazard. Since NMR spectroscopy is an excellent technique for the unambiguous detection of Li metal, we employ it here for studying the Li plating process in operando under different cycling conditions, with varying charging current, voltage and temperature.[1]
The Ni-rich cathode materials LiNi0.8Mn0.1Co0.1O2 (NMC811)[1] and LiNiO2 (LNO) are studied during charge and discharge, illustrating their structural changes as well as the changes of Li-ion mobility with state-of-charge. For the first time, we present well-resolved operando NMR data of LNO/graphite cells. We use this data to refine the description of phase transformations in LNO during (de)lithiation, in particular with respect to changes of Li mobility. Open questions regarding the 7Li solid-state NMR spectra of LixNiO2 are discussed as well.
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