Observing and Quantifying Fracture Dynamics in Solid-State Battery Alloy Anodes with Operando Synchrotron X-Ray Tomography
Authors: Nelson Douglas Lars , Sandoval Stephanie Elizabeth , Thomas Talia A. , Cavallaro Kelsey Anne , McDowell Matthew Todd 
Published: December 2024

Characterizing buried interfaces in solid-state batteries is critical for understanding and enabling this next-generation energy storage technology [1]. X-ray computed tomography (XCT) is a powerful characterization tool owing to its high spatial resolution (<1 µm), non-destructive nature, access to buried interfaces, and three-dimensional imaging capabilities [2]. Additionally, synchrotron-enabled XCT can collect high resolution, three-dimensional datasets with appropriate temporal resolutions to observe the evolution of buried solid-state interfaces under operando conditions [2]. These qualities have been important for revealing the dynamic evolution of excess-lithium metal anodes and anode-less lithium solid-state batteries using synchrotron XCT [3-8].
Synchrotron XCT investigations into the behavior of lithium metal anodes in solid-state batteries have been vital for the research community’s goal of understanding and mitigating degradation of these systems. However, viable lithium anode solid-state batteries are yet to be realized [1]. As a solid-state battery anode, lithium metal is expensive, highly reactive, and prone to dendritic short-circuiting, making it difficult to incorporate into manufacturing systems and unreliable as an anode [9]. Owing to this, alternative solid-state battery anode materials have been proposed. Chief among these are alloy anode materials, such as silicon, tin, and aluminum, which electrochemically alloy and de-alloy with lithium during charge and discharge of the battery, respectively [10]. These materials experience difficulties in conventional liquid electrolyte lithium-ion batteries due to their large volumetric change during electrochemical cycling that constantly exposes new surface area to the highly reactive liquid electrolyte; this consumes the anode material and quickly degrades capacity [11]. With a solid-state electrolyte, however, this effect is mitigated because the solid electrolyte does not flow to contact new surfaces, resulting in less SEI formation [12]. Despite recent performance advancements with alloy anode materials in solid-state batteries [12,13], there is not yet a fundamental understanding of their dynamic evolution and electro-chemo-mechanical behavior in these systems. Most efforts to characterize this behavior have been conducted with ex situ or postmortem imaging techniques that can artificially damage the anode and its interface with the solid electrolyte [12,13].
Here, we use operando synchrotron XCT to non-destructively investigate the morphological evolution of silicon-based anodes in solid-state batteries during electrochemical cycling. Silicon was selected as the alloy anode material owing to its large specific capacity (3579 mAh g-1) and resulting massive volumetric evolution during cycling (>300%) [10]. Utilizing the excellent spatial and temporal resolution of synchrotron XCT, we reveal the dynamic microstructural evolution of silicon-based electrodes during discharge and charge. We observe the formation of cracks within the silicon anode, as well as identifying key fracture mechanisms that govern impedance evolution. Our results provide new understanding of degradation in silicon anode solid-state batteries and give insight into materials design strategies for mitigating degradation. These strategies are expected to improve the performance of silicon anode solid-state batteries by reducing impedance and increasing capacity retention.

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