Real-time 3D imaging of microstructure growth in battery cells using indirect MRI

Abstract

Lithium metal is a promising anode material for Li-ion batteries due to its high theoretical specific capacity and low potential. The growth of dendrites is a major barrier to the development of high capacity, rechargeable Li batteries with lithium metal anodes, and hence, significant efforts have been undertaken to develop new electrolytes and separator materials that can prevent this process or promote smooth deposits at the anode. Central to these goals, and to the task of understanding the conditions that initiate and propagate dendrite growth, is the development of analytical and nondestructive techniques that can be applied in situ to functioning batteries. MRI has recently been demonstrated to provide noninvasive imaging methodology that can detect and localize microstructure buildup. However, until now, monitoring dendrite growth by MRI has been limited to observing the relatively insensitive metal nucleus directly, thus restricting the temporal and spatial resolution and requiring special hardware and acquisition modes. Here, we present an alternative approach to detect a broad class of metallic dendrite growth via the dendrites' indirect effects on the surrounding electrolyte, allowing for the application of fast 3D 1 H MRI experiments with high resolution. We use these experiments to reconstruct 3D images of growing Li dendrites from MRI, revealing details about the growth rate and fractal behavior. Radiofrequency and static magnetic field calculations are used alongside the images to quantify the amount of the growing structures.Li-ion batteries | in situ MRI | dendrite growth L ithium metal is a promising anode material for secondary lithium batteries because it has the highest theoretical specific capacity of possible anode materials (3,860 mAh/g), and the most negative voltage. The metal's use is currently limited due to irregular microstructure buildup on the electrode during charging (1). These mossy, needle-like, or dendritic structures severely compromise battery performance and can eventually penetrate the separator and cause overheating and short circuiting, thus presenting serious safety concerns. Preventing dendrite growth has proven to be extremely challenging, due in part to the current poor understanding of the conditions under which the dendrites' growth is initiated and the factors that contribute to their continued growth (2, 3). The development of new analytical techniques that are sensitive to dendrite growth and amenable to studying electrochemical cells in situ is crucial to future efforts of improving battery designs and performance (4, 5).In situ NMR spectroscopy and MRI are powerful noninvasive methods that can provide time-resolved and quantitative information about the changes within the electrolyte and the electrodes. NMR measurements are sensitive to dendrite growth and are also able to resolve different lithium microstructure morphologies through chemical shift measurements (6-9). MRI approaches provide additional spatial information, allowing specific structural changes ...

Long-run in operando NMR to investigate the evolution and degradation of battery cells

“…The in-operando NMR data showed an almost linear growth and decrease of the Li microstructure signal integral I µL for the second half of charging and the corresponding first half of discharging, respectively, as expected for a constant current experiment 12,29,36 . With one electron at most one Li + ion can be reduced and deposited on the Li-metal electrode and vice versa 42 .…”

“…Such vertically standing battery housings were used for slice selective probing of a LIB in the stray field of a permanent magnet 39,40 and in combination with an additional coil for pulsed field gradients 31,32,41 . Moreover, three-dimensional 1 H MRI was applied to investigate the Li microstructure growth indirectly 42 . Crucial for all types of cell containers are sealing systems, current collector design and the choice of chemically resistant materials.…”

Rechargeable lithium-ion cell state of charge and defect detection by in-situ inside-out magnetic resonance imaging

“…Magnetic resonance (MR) techniques have been developed to measure several different cell properties 4–13 . A fundamental limitation that is difficult to overcome under typical operating conditions is that conductors are not transparent to rf irradiation.…”

“…Often, the cell casing is made of conductive material, such as polymer-lined aluminum in pouch or laminate cells, but also the electrodes preclude the use of conventional MR for realistic or commercial-type cell geometries. Nonetheless, MR has provided important insights into electrolyte behavior, Li-dendrite growth, and other electrochemical effects by the use of custom-built cells, which allow convenient rf access 4–13 .…”

Advances in In Situ Techniques for Characterization of Failure Mechanisms of Li‐Ion Battery Anodes

“…This study revealed that the growth of dendrites is not unidirectional, and after the dendrite growth, the morphology of the already formed structure does not change further throughout the experiment. Meanwhile, radio frequency study was also used in this study to quantify the MRI data obtained from this experiment …”