Investigating Varied Growth Behavior of Lithium Metal in Solid-State Batteries Using Operando X-Ray Tomography

Lithium metal exhibits complex growth and stripping behavior in solid-state batteries, manifesting as dendrite formation, void generation, and varied lithium growth patterns depending on electrochemical conditions and solid-state electrolyte properties. Previous studies utilizing optical microscopy, <i>in situ</i> TEM, cryogenic focused ion beam and X-ray computed tomography have contributed substantially to understanding lithium growth mechanisms.^1-4 However, many investigations concentrate on singular instances or restricted regions. In this work, we leverage <i>operando</i> X-ray computed tomography to comprehensively track and quantify lithium evolution across 2 mm interfaces under diverse deposition and stripping conditions. Specifically, three distinct scenarios were examined in half cells featuring varying solid-state electrolyte (SSE) characteristics: uniform deposition and stripping in a low-impedance cell, extensive dendritic growth in a high-impedance cell, and uniform deposition followed by dendrite growth triggered by higher current densities. The low impedance cell enabled favorable conditions for uniform deposition and stripping across three half cycles. Segmentation revealed expected volume evolution in the working and counter electrode. In stark contrast to uniform lithium growth, the high-impedance cell featured highly dendritic growth dispersed throughout the SSE. This cell utilized a coarse-grained SSE that resulted in poor interfacial contact at the solid-solid interface and in a porous SSE pellet. Throughout deposition, dendritic lithium was observed to grow around pre-existing cracks/pores, often closing them as deposition continued. Segmentation methods were used to track and quantify the evolution of lithium throughout the first cycle, finding that ~20% of the mechanical damage was irreversible after the first cycle. Finally, we also observed that dendritic networks grow near the edges of another cell at higher current densities after initially growing uniformly, indicating different chemo-mechanics at the cell boundary. Collectively, the lithium growth behavior captured and reported here enhance our understanding of the diversity of evolution of lithium in SSBs.<br/><br/><br/>1. Kazyak, E. <i>et al.</i> Understanding the electro-chemo-mechanics of Li plating in anode-free solid-state batteries with operando 3D microscopy. <i>Matter</i> <b>5</b>, 3912–3934 (2022).<br/>2. Wang, Z. <i>et al.</i> In situ STEM-EELS observation of nanoscale interfacial phenomena in all-solid-state batteries. <i>Nano Lett.</i> <b>16</b>, 3760–3767 (2016).<br/>3. Sandoval, S. E. <i>et al.</i> Structural and electrochemical evolution of alloy interfacial layers in anode-free solid-state batteries. <i>Joule</i> <b>7</b>, 2054–2073 (2023).<br/>4. Ning, Z. <i>et al.</i> Dendrite initiation and propagation in lithium metal solid-state batteries. <i>Nature</i> <b>618</b>, 287–293 (2023).