In-Situ Quasi-Simultaneous Neutron and X-Ray Tomography of Current Collector-Solid Electrolyte Interfaces in Anode-Free Solid-State Batteries

Anode-free solid-state batteries (AF-SSBs) consisting of a metallic current collector (CC) (e.g., stainless steel) as the anode are a promising next-generation battery technology for sustainable electric vehicles (EVs).¹ In comparison to conventional Li-ion batteries, AF-SSBs can potentially provide high energy and power densities, improve battery safety and recyclability, and lower manufacturing costs.² However, they suffer from significant anode/interfacial instabilities that have impeded their practical realizations.³Particularly, a key challenge facing AF-SSBs is poor chemo-mechanical stability of the CC|solid electrolyte (SE) interface.^3-4 More specifically, the 3D morphological behavior of the CC|SE interface and bulk SE upon Li plating is unknown. The localized and buried nature of the CC|SE interface makes it extremely challenging to characterize.⁵<br/><br/>In this work, we leverage the sensitivity of neutrons to Li and X-rays to metallic CC to conduct in-situ 3D characterization of interfacial degradation of CC|SE interface in AF-SSBs using quasi-simultaneous neutron and X-ray micro-computed tomography (µCT). Here, we used the word “quasi” as we conducted X-µCT first, then a high-resolution neutron-µCT from the exact same sample location at the same imaging beamline. Weperformed our experiments at the NeXT-Grenoble beamline⁶ at Institut Laue-Langevin, France. Our effective spatial resolution for the neutron-µCT was ~ 5 um — state-of-the-art in the world. We imaged three batteries in the following states: (1) pristine, and after plating at (2) low current density (0.5 µA) and (3) high current density (5 µA). High current density was chosen as it results in high overpotential, leading to Li dendrite formation during battery cycling.<br/><br/>Our X-µCT data shows interfacial contact loss between the stainless steel (SS) CC and the Li₆PS₅Cl electrolyte as well as void formation at the CC|SE interface. Additionally, our X-µCT data reveals pre-existing cracks in the SE pellet in the pristine cell. Though the cracks in the pristine cell were smaller as compared to those observed in the cells cycled at low and high current densities. Using the neutron-µCT data, we are characterizing the 3D morphological behavior and spatial heterogeneities of plated Li on CC at low and high current densities. Overall, these results will help us understand the chemo-mechanical instabilities of the CC|SE interface caused by poor Li⁺ ionic transport. We believe these insights will guide the design of chemo-mechanically stable CC|SE interfaces for AF-SSBs for sustainable EVs.<br/><br/><b>References: </b><br/>1. Nanda, J., Wang, C., & Liu, P. (2018). Frontiers of solid-state batteries. <i>MRS Bulletin</i>, <i>43</i>(10), 740-745.<br/>2. Herle, S., Chen, Z., Libera, J., ... & Sakamoto, J. (2020). <i>Challenges for and Pathways Toward Solid-State Batteries</i> (No. ORNL/TM-2020/1747). Oak Ridge National Lab.(ORNL), Oak Ridge, TN (United States).<br/>3. Kazyak, E., Wang, ... & Dasgupta, N. P. (2022). Understanding the electro-chemo-mechanics of Li plating in anode-free solid-state batteries with operando 3D microscopy. <i>Matter</i>, <i>5</i>(11), 3912-3934.<br/>4. Hatzell, K. B., Chen, X. C., Cobb, C. L., Dasgupta, N. P., Dixit, M. B., Marbella, L. E., ... & Zeier, W. G. (2020). Challenges in lithium metal anodes for solid-state batteries. <i>ACS Energy Letters</i>, <i>5</i>(3), 922-934.<br/>5. Yu, Z., Zhang, X., Fu, C., ... & Wang, J. (2021). Dendrites in solid state batteries, ion transport behavior, advanced characterization, and interface regulation. <i>Advanced Energy Materials</i>, <i>11</i>(18), 2003250.<br/>6. Tengattini, A., Lenoir, N., Andò, E., Giroud, B., Atkins, D., Beaucour, J., & Viggiani, G. (2020). NeXT-Grenoble, the Neutron and X-ray tomograph in Grenoble. <i>Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment</i>, <i>968</i>, 163939.<br/><br/><b>Keywords:</b> Plated Lithium; Neutron imaging; X-ray imaging; Anode-free; Solid-state batteries