Mechanical stress plays a critical role in the degradation of battery electrodes, particularly in high-capacity materials such as silicon anodes and high-nickel cathodes. Repeated cycling induces volume changes, leading to particle cracking, binder degradation, and electrode delamination. These mechanical failure modes reduce active material availability, increase impedance, and ultimately shorten battery life. Understanding and modeling these phenomena require a combination of continuum mechanics and fracture mechanics approaches, validated by experimental techniques such as X-ray tomography and strain gauges.

Particle cracking occurs due to the repeated expansion and contraction of active materials during lithiation and delithiation. Silicon, for example, undergoes a volume change of up to 300%, while high-nickel cathodes experience more modest but still significant strain. These volume variations generate internal stresses that exceed the fracture toughness of the material, leading to crack initiation and propagation. Continuum mechanics models, such as finite element analysis (FEA), simulate stress distributions within particles by solving coupled mechanical and diffusion equations. These models incorporate material properties like Young’s modulus, Poisson’s ratio, and fracture energy to predict crack formation. For instance, FEA has shown that silicon particles larger than a critical size (typically around 150-300 nm) are more prone to fracture due to higher stress concentrations at the particle core.

Fracture mechanics models complement continuum approaches by explicitly accounting for crack growth. The phase-field fracture method is widely used to simulate crack propagation without predefined paths. This technique introduces a continuous field variable to represent cracks, allowing for complex fracture patterns. Studies applying phase-field models to silicon anodes have demonstrated that crack networks evolve cyclically, with new cracks forming in each charge-discharge cycle. Additionally, cohesive zone models (CZMs) describe interfacial debonding between particles and binders, capturing the progressive loss of mechanical integrity.

Binder degradation is another critical failure mode, particularly in electrodes with large volume changes. Polymeric binders, such as polyvinylidene fluoride (PVDF) or carboxymethyl cellulose (CMC), mechanically stabilize the electrode by adhering active particles to the current collector. However, cyclic stresses weaken binder bonds, leading to particle isolation and capacity fade. Continuum models treat binders as viscoelastic materials, incorporating time-dependent deformation and damage accumulation. For example, a Prony series can represent the relaxation behavior of binders under stress, while damage models quantify bond breakage over cycles. Experimental studies using atomic force microscopy (AFM) have measured binder stiffness degradation, confirming model predictions that binder performance declines after repeated strain.

Electrode delamination occurs when the active layer separates from the current collector due to interfacial stresses. This failure mode is particularly severe in thick electrodes or those with poor adhesion. Finite element models simulate delamination by modeling the electrode-current collector interface with cohesive elements. Parameters such as interfacial strength and fracture energy are calibrated using peel tests or other mechanical characterization methods. Research has shown that delamination is more likely in electrodes with high active material loading, where stress concentrations are amplified. For instance, simulations of silicon anodes with 80% active material content predict delamination after as few as 50 cycles under typical operating conditions.

Quantifying cycling-induced volume changes is essential for accurate degradation modeling. For silicon anodes, experimental techniques such as in-situ X-ray tomography track particle expansion in 3D, revealing heterogeneous strain distributions. Digital volume correlation (DVC) processes these images to compute displacement fields, validating mechanical models. Similarly, strain gauges embedded in electrodes provide real-time measurements of macroscopic deformation. High-nickel cathodes, though less extreme in volume change, still require precise strain measurement due to their sensitivity to mechanical degradation. Neutron diffraction has been used to map lattice strains in nickel-manganese-cobalt (NMC) cathodes, showing that local stresses vary with state of charge.

Model validation relies on correlating simulated stress states with observed degradation. X-ray tomography identifies crack locations and densities, which can be compared to FEA predictions. For example, a study on silicon-graphite composite anodes found that cracks preferentially initiated at silicon-graphite interfaces, matching simulated stress hotspots. Similarly, scanning electron microscopy (SEM) post-mortem analysis reveals binder fracture patterns consistent with viscoelastic damage models. Electrochemical impedance spectroscopy (EIS) further links mechanical degradation to performance loss, as increased particle isolation raises interfacial resistance.

Advanced modeling techniques are improving predictive accuracy. Multiscale approaches combine particle-level fracture models with homogenized electrode-scale simulations, capturing both local and bulk effects. Machine learning accelerates parameter optimization by identifying key material properties from experimental datasets. Digital twins integrate real-time sensor data with mechanical models, enabling adaptive control strategies to mitigate stress-induced degradation.

In summary, mechanical stress-induced degradation in battery electrodes is a multifaceted problem requiring integrated modeling and experimental validation. Continuum and fracture mechanics approaches provide insights into particle cracking, binder degradation, and delamination, while advanced characterization techniques ensure model fidelity. As batteries push toward higher energy densities, understanding and mitigating mechanical failure will remain crucial for durability and performance.