(398c) Lithium Plating Detection during Extreme Fast Charging in Lithium-Ion Batteries Using Simultaneous Neutron and X-Ray Imaging

Lithium-ion batteries (LIBs) have profoundly advanced the development of electric vehicles (EV). However, one of the remaining bottlenecks in the widespread deployment of EVs is the long charging time required for these commercial LIBs. There is a global push towards extreme fast charging (XFC) to reduce their charging times to 10-15 minutes¹. However, XFC results in severe degradation in the electrochemical performance of batteries. This is mainly attributed to the loss of active Li, either as “dead” which has become electronically disconnected after plating on the anode or as “inactive” due to the irreversible reaction of Li with the electrolyte to form a solid electrolyte interphase. Since parasitic lithium plating is one of the identified major results of XFCBs², understanding its origin and characteristics is important to developing strategies to enable fast-charged batteries. Several studies have characterized Li plating during XFC using techniques such as cryo-electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray micro-computed tomography (CT) among others³. While valuable, these characterization techniques have limitations⁴ in terms of their sample preparation, imaging resolution, and the image contrast required to distinguish between materials of similar atomic number (Z).

Here, we are using simultaneous neutron and X-ray-based dual-mode micro-computed tomography, an alternative, non-destructive imaging modality, to investigate the characteristics of Li plating during XFC in LIBs. Since X-rays and neutrons are sensitive to the electron and nuclear density of the material respectively, dual-mode X-ray and neutron CT offers advantageous to readily separate the different anode components in a LIB such as Li, graphite, and pores due to the complementary interaction of the two imaging probes with matter. Higher energy X-rays are needed to get through the metallic components in batteries such as copper and aluminum. However, they do not have sufficient contrast to separate lithium from graphite. Thus, neutrons are used due to their high sensitivity to lighter elements such as lithium, especially ⁶Li, and carbon.

We performed the multi-modal imaging experiments at the Neutron and X-ray Tomography (NeXT) ⁵ system located on the BT-2 beamline at National Institute of Standards and Technology Center for Neutron Research. We characterized pristine and cycled graphite anode strips containing plated lithium at different regions. For cycled anode strips, we disassembled the battery pouch cells and used the graphite anodes cycled under XFC conditions for 450 cycles at fully discharged condition. These strips were used to get sample sizes small enough to achieve the highest possible spatial resolution. In addition, we characterized an uncycled single-layer battery pouch cell containing electrolyte for which we rolled the battery cell in the form of a cylinder to put in the beam path. The spatial resolution achieved by this technique was ~10-15 μm, thus providing sufficient resolution to pinpoint the location of Li plating within the thickness of the anode. We are using image processing algorithms and bivariate histogram segmentation to process these dual-imaging datasets to investigate whether a link exists between the spatial heterogeneity of Li plating and the local microstructure of the battery anode such as porosity, tortuosity, and thickness. We are interested in understanding why and where Li plating occurs on the battery anode. Addressing these fundamental questions will inform improved battery designs, graphite anode architectures, and charging protocols that will reduce Li plating during XFC in LIBs. We envisage that these findings will help make charging an EV similar to filling up at a gas station.

References:

1. Liu, Y., Zhu, Y., & Cui, Y. (2019). Challenges and opportunities towards fast-charging battery materials. Nature Energy, 1.
2. Tomaszewska, A., Chu, Z., Feng, X., O'Kane, S., Liu, X., Chen, J., ... & Li, Y. (2019). Lithium-ion battery fast charging: A review. eTransportation, 1, 100011.
3. Lu, J., Wu, T., & Amine, K. (2017). State-of-the-art characterization techniques for advanced lithium-ion batteries. Nature Energy, 2(3), 17011.
4. Li, Y., Li, Y., & Cui, Y. (2018). Catalyst: how cryo-EM shapes the development of next-generation batteries. Chem, 4(10), 2250-2252.
5. LaManna, J. M., Hussey, D. S., Baltic, E., & Jacobson, D. L. (2017). Neutron and X-ray Tomography (NeXT) system for simultaneous, dual modality tomography. Review of Scientific Instruments, 88(11), 113702.