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Evelyna Wang

Publications and source records attributed to Evelyna Wang.

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Bridging electrode preparation and electrocatalyst performance with physics-based causal AI

State-of-the-art artificial intelligence (AI) and Machine-Learning (ML) tools have not yet enabled rapid design of next-generation materials. Detailed physical understanding of how material properties affect device performance is required to advance materials development. For example, optimization of ink parameters for electrocatalysts has no known physical mathematical model and thus insights are difficult to translate from material studies to device studies. Herein, we demonstrate how to use the emerging AI tool, physics-based structural causal models (SCMs), to extract quantitative causative insights from complex heterogeneous electrochemical systems with small (n < 10), but multi-modal datasets (modes > 10). Our SCM quantitatively separates the role that varying the support-to-catalyst ratios and total material loadings plays on catalytic performance. The proof of concept model developed in this work enables root-cause-analysis on the cyclic voltammograms of manganese-antimony oxide oxygen reduction electrocatalysts on Vulcan carbon supports tested in alkaline media using a rotating disc electrode device configuration. Our preliminary causal analyses quantitatively disentangle how the catalyst performance is affected by the number of active sites versus the thickness of the electrode. To the best of our knowledge, this is the first demonstration of physics-based SCMs applied to electrochemical materials and their performance.

cond-mat.mtrl-sci

Quantifying the reactivity of isolated LixSi domains in Si anodes using operando NMR

The use of Si anodes can greatly improve the energy density of Li-ion batteries. However, understanding and mitigation of calendar aging remains a barrier to commercialization. In this short report, we utilize operando Nuclear Magnetic Resonance (NMR) spectroscopy to detect and quantify lithium silicides (LixSi) as they form and react within Si anodes in pouch cells during calendar aging. We provide direct experimental evidence of complex aging phenomena in the Si anodes, including both SEI growth and dissolution during storage. Formation of electrochemically isolated LixSi is also observed, as indicated by the partial persistence of highly lithiated phases after the cell is discharged. Remarkably, we show that these isolated domains can themselves self-discharge over time, suggesting that their detection can be challenging in post-mortem studies. Finally, we show that aging outcomes depend heavily on the type of silicon particles contained within the electrode, and that certain surface coatings can help decrease the reactivity between lithium silicides and the electrolyte.

cond-mat.mtrl-sci

Building high-energy silicon-containing batteries using off-the-shelf materials

The technology of silicon anodes appears to be reaching maturity, with high-energy Si cells already in pilot-scale production. However, the performance of these systems can be difficult to replicate in academic settings, making it challenging to translate research findings into solutions that can be implemented by the battery industry. Part of this difficulty arises from the lack of access to engineered Si particles and anodes, as electrode formulations and the materials themselves have become valuable intellectual property for emerging companies. Here, we summarize the efforts by Argonne's Cell Analysis, Modeling, and Prototyping (CAMP) Facility in developing Si-based prototypes made entirely from commercially available materials. We describe the many challenges we encountered when testing high-loading electrodes (> 5 mAh/cm2) and discuss strategies to mitigate them. With the right electrode and electrolyte design, we show that our pouch cells containing > 70 wt% SiOx can achieve 600-1,000 cycles at C/3 and meet projected energy targets of 700 Wh/L and 350 Wh/kg. These results provide a practical reference for research teams seeking to advance silicon-anode development using accessible materials.

cond-mat.mtrl-sci