arXiv subjects

William Chueh

Publications and source records attributed to William Chueh.

3 recordsLinked to original sources

arXiv2026

Operando spectro-ptychography reveals dynamical charge-storage and degradation pathways in redox-active electrodes

Electrochemical reactions at buried electrode-electrolyte interfaces govern how redox-active materials store and release energy. However, these reactions are difficult to visualize because chemical and morphological changes occur simultaneously over distinct length and time scales. Existing operando microscopies often require trade-offs among chemical sensitivity, spatial resolution and temporal resolution. Direct nanoscale tracking of such processes throughout extended timescale has therefore remained out of reach. Here, we develop a fast and robust operando soft X-ray spectro-ptychography platform that delivers chemical-state-resolved spatiotemporal movies of redox-active electrodes over the full battery lifetime. Applied to an alkaline Fe anode, the method reveals that reversible charge storage gives way to degradation through two competing processes: rapid hydroxide insertion that drives early reversible cycling, and slower dissolution-redeposition that redistributes Fe, enlarges FeOOH particles, and ultimately causes capacity loss. By separating fast charge-storage chemistry from slower degradation chemistry in operando and at both single-particle and particle ensemble level, this work establishes spectro-ptychography as a general approach for studying dynamic redox transformations in batteries, electrocatalysts, and other electrochemical materials.

cond-mat.mtrl-sci↗

arXiv2025

Securing the supply of graphite for batteries

Surging demand for graphite in energy storage applications has led to concerns about supply chai security for manufacturers and nations globally. Currently, China produces over 92% of graphite for anodes, posing a risk for industries reliant on graphite supply. Here, we systematically assess the costs of producing natural and synthetic battery-grade graphite in the U.S. and China using process-based cost models. We find that production costs in the U.S. are higher than those in China by 100-200%, so scaling production in the short-term will require significant policy support. We use our models to explore opportunities to improve the competitiveness of graphite production outside China, finding that lower financing rates and improved shaping yields can together reduce costs by 25-30%. Further implementing other cost reduction strategies, such as improving process throughput or lowering equipment costs, can achieve 35-40% lower costs. Finally, we discuss how innovative graphite production processes like methane pyrolysis and catalytic graphitization may provide competitive pathways.

econ.GN↗

arXiv2018

Best arm identification in multi-armed bandits with delayed feedback

We propose a generalization of the best arm identification problem in stochastic multi-armed bandits (MAB) to the setting where every pull of an arm is associated with delayed feedback. The delay in feedback increases the effective sample complexity of standard algorithms, but can be offset if we have access to partial feedback received before a pull is completed. We propose a general framework to model the relationship between partial and delayed feedback, and as a special case we introduce efficient algorithms for settings where the partial feedback are biased or unbiased estimators of the delayed feedback. Additionally, we propose a novel extension of the algorithms to the parallel MAB setting where an agent can control a batch of arms. Our experiments in real-world settings, involving policy search and hyperparameter optimization in computational sustainability domains for fast charging of batteries and wildlife corridor construction, demonstrate that exploiting the structure of partial feedback can lead to significant improvements over baselines in both sequential and parallel MAB.

cs.LG↗