Effective Characterization, Mitigation, and Modeling of Cycle Life and Thermal Degradation in High-Performance Lithium-Ion Battery Systems

Abstract

As lithium-ion (Li-ion) battery technologies continue to evolve, delivering higher energy and power densities, the importance of design optimization for achieving safer, high-performance battery systems continues to grow. This dissertation analyzes the dynamic interplay between three phenomena: heat generation, heat dissipation, and degradation kinetics. These three interdependent phenomena form a feedback loop that critically influences the operational safety and longevity of Li-ion battery systems. When heat generated within the cell exceeds heat dissipated from the cell, degradation accelerates. This in turn increases internal resistance within the cell and further intensifies heat generation. Understanding the dynamics of these phenomena is essential for optimizing battery pack design. Through experimentally validated heat transfer models, this work evaluates the thermal response of two battery block structures under various amounts of thermal stress produced by both Joule heating and exothermic reaction energies. Notably, battery blocks with high thermal conductance and integrated latent heat capacity, such as the microfibrous mesh/phase change material (MFM/PCM) block, demonstrate superior thermal accommodation and operational stability under aggressive cycling conditions. While aluminum blocks offer effective thermal isolation between cells, their limited dissipation capacity leads to accelerated degradation in high C-rate applications, especially in aged cells. This highlights the need for thermal isolation within thermally conductive blocks to prevent cascading failure within the pack while also limiting degradation kinetics within the cell. Due to the inherent failure risk, a novel methodology is developed in this work to conservatively estimate worst-case scenario failure energy using only the mass and composition of cell components, eliminating the need for destructive testing. This approach enables scalable, geometry-independent safety analysis for various battery chemistries, while incorporating atmospheric conditions that significantly influence failure severity. Cascade-resistant battery pack designs are also explored due to the severity of a single-cell failure event. This work shows that while high thermal conductance aids in dissipating heat from failed cells, it can inadvertently expose neighboring cells to elevated temperatures. The MFM/PCM block mitigates this risk by combining latent heat absorption with effective thermal conductance, thereby preventing thermal runway propagation. Cascading failure prevention is further explored by implementing degradation reaction kinetics within the battery block while it is under load leading to an organically triggered failure event in an end-of-life (EOL) cell. The MFM/PCM block effectively dissipates and absorbs the heat generated by both Joule heating and exothermic degradation reactions, preventing cascading failure in an active system operated at elevated C-rates. The key contributions of this work include methodological advances in battery pack design, integration of aging and thermal degradation kinetics into operational battery block simulations, the development of simplified failure energy estimation methods, and the modeling of multi-chemistry thermal responses. These developments collectively define a design trade space for Li-ion battery systems that balances performance, safety, and longevity.