7Li MRI of Li batteries reveals location of microstructural lithium

Abstract

There is an ever-increasing need for advanced batteries for portable electronics, to power electric vehicles and to facilitate the distribution and storage of energy derived from renewable energy sources. The increasing demands on batteries and other electrochemical devices have spurred research into the development of new electrode materials that could lead to better performance and lower cost (increased capacity, stability and cycle life, and safety). These developments have, in turn, given rise to a vigorous search for the development of robust and reliable diagnostic tools to monitor and analyse battery performance, where possible, in situ. Yet, a proven, convenient and non-invasive technology, with an ability to image in three dimensions the chemical changes that occur inside a full battery as it cycles, has yet to emerge. Here we demonstrate techniques based on magnetic resonance imaging, which enable a completely non-invasive visualization and characterization of the changes that occur on battery electrodes and in the electrolyte. The current application focuses on lithium-metal batteries and the observation of electrode microstructure build-up as a result of charging. The methods developed here will be highly valuable in the quest for enhanced battery performance and in the evaluation of other electrochemical devices.

Visualizing skin effects in conductors with MRI: 7Li MRI experiments and calculations

“…Similar assignments have also been made in battery systems, where Li-microstructures growing perpendicular to the surface of the electrode have been shown to display a significant shift away from the bulk metal peak [19,21], and where orientation-dependent bulk magnetic susceptibility effects have been explored [39]. In non-conducting samples, the latter leads to a broadening of the spectrum as the shifts vary continuously from one part of the sample to another.…”

“…Here, the use of conducting components is clearly a requirement. Indeed, in situ NMR [19,20] and MRI [21,22] of functioning Li-metal batteries have given great insight into properties of the electrolyte and the metal electrodes during the charge cycles in such systems. The strong susceptibility effects associated with the regions surrounding the Li-metal have even proven to be advantageous for such studies, as they give rise to distinct and characteristic chemical shifts for surface microstructures and dendrites [19,21].…”

“…some of their characteristics. In previous studies, qualitative rules have been followed to align the main face of the (square) conducting metal electrodes with the RF field direction in order to minimize RF field inhomogeneities, but the RF field dependence on orientation and shape were not known [21,23,24]. In this work, we combine RF field and bulk magnetic susceptibility calculations with experimental NMR and MRI results to clarify the role of the RF-field orientation, skin effects, and susceptibility shifts in determining the appearance of spectra and images of bulk metals and samples that contain them.…”

In situ methods for Li-ion battery research: A review of recent developments

“…In particular techniques that are capable of providing information on the 3D morphology of electrodes as well as the chemical composition have shown to be extremely insightful [28,40,82,83] and further development is therefore expected. Furthermore, in operando measurements, probing the non-equilibrium states, require a high data collection rate, which is presently challenging for several in situ tools.…”

“…By applying NMR in the way discussed above, Chandrashekar et al [83] measured the amount of deposited Li-microstructures during electrochemical cycling in a symmetric lithium cell. However, to determine the location of the lithium deposits, magnetic resonance imaging (MRI) was employed to obtain a three dimensional image.…”