We will describe our work on the development of techniques for assessing Li-ion batteries and battery materials via magnetic resonance imaging (MRI). The goal of these studies is to analyze battery degradation and energy storage mechanisms in situby imaging changes in both the electrolyte and the electrodes in a noninvasive fashion while a cell is charged or discharged.

We will discuss recent breakthroughs we have made in performing MRI experiments on commercial pouch and coin cell batteries that allow diagnostic tests to be obtained without disassembling the cells. These tests can be run in situ or ex situ and can be used to indicate cycling properties of new battery components, to give a ‘fingerprint’ of manufactured cells for comparison and quality control purposes, or to offer engineering insights into the physical properties of the battery.

We will also report on specific applications of MRI in functioning lithium metal batteries [1], where the technique can be used to correlate the behavior of the electrolyte concentration gradient to the type and rate of dendrite growth on the surface of the Li metal electrode. These studies have confirmed the existence of separate growth mechanisms in different charging regimes. The methodology is extremely sensitive to Li dendrite formation, opening the possibility of testing a broad range of materials and operating conditions to understand when dendrites grow and how they can be prevented.

By developing a detailed understanding of the impact lithium dendrites have on their surroundings, we have been able to design fast 1H MRI experiments that are extremely sensitive to local dendrite growth [2]. The experiments allow for the 3D structure of the dendrites to be reconstructed, and are fast enough to capture the dendrite growth in real time, shedding light on the growth behavior, rate and morphology of the structures formed. Moreover, through simulations and a detailed analysis of the results obtained, we show how the MRI can be used to quantify the volume of dendrites grown.

1. Chang, H. J.; Ilott, A. J.; Trease, N. M.; Mohammadi, M.; Jerschow, A.; Grey, C. P. J. Am. Chem. Soc. 2015, 137(48), 15209–15216.

2. Ilott, A. J.; Mohammadi, M.; Chang, H. J.; Grey, C. P.; Jerschow; Proc. Natl. Acad. Sci. 2016 113 (39), 10779–10784.

Figure caption: Regions of microscopic lithium dendrites that have grown between two lithium metal electrodes. The image is reconstructed from a 15 minute ¹H MRI scan.