Theory of SEI Formation in Rechargeable Batteries: Capacity Fade, Accelerated Aging and Lifetime Prediction (1210.3672v3)

Abstract: Cycle life is critically important in applications of rechargeable batteries, but lifetime prediction is mostly based on empirical trends, rather than mathematical models. In practical lithium-ion batteries, capacity fade occurs over thousands of cycles, limited by slow electrochemical processes, such as the formation of a solid-electrolyte interphase (SEI) in the negative electrode, which compete with reversible lithium intercalation. Focusing on SEI growth as the canonical degradation mechanism, we show that a simple single-particle model can accurately explain experimentally observed capacity fade in commercial cells with graphite anodes, and predict future fade based on limited accelerated aging data for short times and elevated temperatures. The theory is extended to porous electrodes, predicting that SEI growth is essentially homogeneous throughout the electrode, even at high rates. The lifetime distribution for a sample of batteries is found to be consistent with Gaussian statistics, as predicted by the single-particle model. We also extend the theory to rapidly degrading anodes, such as nanostructured silicon, which exhibit large expansion on ion intercalation. In such cases, large area changes during cycling promote SEI loss and faster SEI growth. Our simple models are able to accurately fit a variety of published experimental data for graphite and silicon anodes.

• The paper introduces a comprehensive mathematical model using a single-particle framework to explain lithium-ion battery capacity fade based on SEI formation and loss of active lithium.
• The model predicts homogeneous SEI growth across electrodes, even at high rates, and incorporates temperature dependence via an Arrhenius relationship for accelerated aging predictions.
• This physics-based model shifts diagnostics and design from empirical methods, though materials like silicon pose challenges due to stress-accelerated SEI growth.

Theory of SEI Formation in Rechargeable Batteries: Capacity Fade, Accelerated Aging, and Lifetime Prediction

The paper authored by Matthew B. Pinson and Martin Z. Bazant aims to provide a comprehensive mathematical model explaining capacity fade and lifetime prediction in lithium-ion batteries, focusing on the formation of the solid-electrolyte interphase (SEI) as a principal mechanism of capacity fade. This phenomenon is a critical and prevalent concern in the field of battery technology, particularly due to its impact on the lifecycle of commercial lithium-ion cells.

The authors tackle the intricate process of SEI formation using a single-particle model, which offers predictive insights into capacity degradation by considering the loss of lithium ions to SEI growth at the negative electrode. Their approach models capacity fade by assuming a relatively uniform and homogeneous SEI layer throughout the electrode, relying on a set of simplifying assumptions such as negligible solid deformation and a constant base reaction rate.

The paper extends this conceptual framework to porous electrodes to investigate potential spatial dependencies in SEI formation. Remarkably, the proposed model suggests that SEI growth remains homogeneous even under high discharge rates, an insight that significantly simplifies the challenges of modeling complex electrode systems. Additionally, the framework reveals that SEI growth is Gauss-normal distributed in its statistics, confirming with experimental data.

The implications of this work are noteworthy for practical applications, signaling a move towards physics-based modeling as opposed to purely empirical methodologies. This shift promises significant advancements in battery diagnostics, accelerated aging tests, and materials design aimed at prolonging battery life.

The authors also address the complex challenge posed by rapidly degrading anodes like nanostructured silicon, which undergo significant expansion during lithium intercalation. They emphasize that such materials, despite their potential for high energy density, suffer from faster SEI growth and capacity loss driven by substantial mechanical stresses. The theoretical extension suggests potential areas for future experimental efforts to better stabilize these materials through engineering SEI formation.

A key aspect of the paper is its emphasis on temperature as a critical factor influencing SEI formation and consequently battery aging. The authors employ an Arrhenius relationship to model the temperature dependence of SEI diffusivity, offering a sophisticated tool for predicting capacity fade across varying temperatures. This capability is critical for estimating battery life using data from accelerated aging experiments conducted at elevated temperatures.

The paper concludes by exploring the importance of SEI in mitigating solvent decomposition at the electrode interface, a protective role that must be optimized to achieve long-lasting battery performance. The authors suggest potential applicability of their findings to other battery systems, thus opening avenues for future research while providing a robust platform to guide the development of advanced rechargeable battery technologies.

Overall, the work of Pinson and Bazant presents a significant contribution to the battery modeling literature, providing a rigorously derived theoretical framework that not only matches experimental data but also enables broad application in the design and evaluation of emerging battery technologies.