Damage characterization and its coupling to electrochemistry in battery cathodes

The degradation of Li-ion battery cathodes is governed by a complex and tightly coupled interplay between mechanical damage and electrochemical degradation processes. During repeated cycling, lithium insertion and extraction generate lattice deformations and mechanical stress, resulting in cracking, pulverization, and structural disintegration of cathode particles. These mechanical failures hinder lithium-ion transport and alter interfacial charge transfer kinetics. At the same time, chemical degradation mechanisms, including charge heterogeneity, surface reconstruction, and parasitic side reactions, emerge and interact with mechanical damage. This multi-physics coupling significantly affects capacity retention, rate performance, and long-term stability of battery cells.

While extensive research has been conducted on the electrochemical performance of Li-ion battery cathodes, there remains a critical gap in understanding the mechanical degradation mechanisms and their coupling with electrochemical processes. Existing models often neglect the complex interplay between mechanical damage, lithium diffusion, surface chemistry, and electrolyte interactions—processes that are essential for predicting long-term battery behavior. Moreover, experimental characterization of mechanical properties at the particle level, particularly across different microstructures, is limited, yet crucial for understanding fracture and failure. This thesis addresses these gaps by: (1) developing a comprehensive computational framework for coupled mechanical damage and electrochemistry; (2) uncovering key mechanisms of electro-mechanical degradation through multi-physics modeling; and (3) experimentally quantifying the structure–property relationships of cathode particles to inform material design.

This dissertation focuses on the characterization of mechanical damage and its coupling to electrochemical behavior in layered cathode materials, particularly LiNixMnyCozO₂ (NMC). Chapter 1 introduces the background of Li-ion battery operation, mechanical degradation mechanisms, and experimental characterization methods. In Chapter 2, a computational framework is developed to model coupled mechanical damage and electrochemical transport, along with an overview of mechanical property measurement, specifically for particle systems studies in this dissertation. Chapter 3 investigates how anisotropic material properties influence stress evolution and their impact on lithium diffusion. Chapter 4 examines the mutual modulation between surface chemistry and bulk mechanical degradation. Chapter 5 explores electrolyte infiltration along cracks using the fully coupled mechanical damage and electrochemistry model. Chapter 6 links mechanical properties to chemomechanical degradation across different microstructures, utilizing experimental nanoindentation to evaluate particle strength, elastic modulus, and fracture energy. Finally, Chapter 7 assesses the role of surface coatings in enhancing structural stability through improved charge distribution and mechanical confinement.

This work provides a unified computational–experimental approach to characterize damage mechanisms and their electrochemical consequences in cathodes. The findings offer mechanistic insights and design principles for developing more robust, long-life Li-ion battery materials.