Mechanical stress in multilayer battery electrodes can lead to delamination, a critical failure mode that degrades performance and lifespan. The interfaces between active material layers, current collectors, and binders are particularly vulnerable to stress-induced separation. Understanding and modeling this phenomenon requires a focus on adhesion energy and interfacial failure mechanics, using methods like cohesive zone modeling (CZM) and J-integral analysis. These approaches provide insights into the conditions under which delamination occurs and how to mitigate it.

Multilayer electrodes consist of multiple material layers, each with distinct mechanical properties. During battery operation, repeated lithiation and delithiation cause volume changes in active materials, generating internal stresses. These stresses accumulate over cycles, leading to interfacial cracks and eventual delamination. The adhesion energy between layers determines the resistance to such failure. Adhesion energy is the work required to separate two bonded surfaces, typically measured in J/m². For electrode materials, this energy depends on factors like surface roughness, binder composition, and processing conditions.

Cohesive zone modeling is a widely used method to simulate delamination. CZM represents the interface as a fictitious material with a traction-separation law that defines its behavior under stress. The law includes parameters like peak traction (maximum stress before damage initiates) and critical fracture energy (energy required for complete separation). For example, a typical graphite anode’s interface with a copper current collector may have a peak traction of 10–20 MPa and a critical fracture energy of 5–50 J/m², depending on binder type and electrode processing. The model divides the failure process into three stages: elastic deformation, damage initiation, and progressive softening until complete separation.

J-integral analysis offers an alternative approach, rooted in fracture mechanics. It quantifies the energy release rate at a crack tip, providing a criterion for crack propagation. When the J-integral value exceeds the material’s critical adhesion energy, delamination occurs. This method is particularly useful for evaluating interfacial toughness in multilayer systems. For instance, studies on NMC cathodes have shown J-integral values ranging from 10 to 100 J/m², influenced by binder concentration and electrode porosity.

Interfacial failure modes in electrodes can be categorized into three types: adhesive failure (separation at the interface), cohesive failure (rupture within the weaker material), and mixed-mode failure (a combination of both). Adhesive failure often dominates in electrodes with poor binder adhesion, while cohesive failure occurs when the binder or active material itself fractures. Mixed-mode failure is common in real-world scenarios, where mechanical loading is rarely uniaxial. The mode mixity ratio, describing the proportion of normal to shear stress, affects the critical energy release rate. Experimental data suggest that a 50% mode mixity can reduce the critical energy by 20–30% compared to pure mode I (normal stress) loading.

Material properties significantly influence delamination resistance. For example, polyvinylidene fluoride (PVDF) binders typically provide higher adhesion energy (20–40 J/m²) than carboxymethyl cellulose (CMC) binders (5–15 J/m²). Similarly, electrodes with higher porosity exhibit lower interfacial strength due to reduced contact area. Calendering pressure during manufacturing also plays a role; excessive pressure may improve initial adhesion but introduce residual stresses that accelerate delamination over cycles.

Environmental factors like temperature and humidity further complicate the picture. Elevated temperatures can soften binders, reducing interfacial strength, while humidity may degrade adhesion through moisture absorption. For instance, PVDF-based interfaces lose up to 30% of their adhesion energy at 60°C compared to room temperature. Such effects must be accounted for in models to ensure accurate predictions under real-world conditions.

Model validation requires coupling simulations with experimental techniques like peel tests, scratch tests, or double cantilever beam (DCB) experiments. Peel tests measure the force required to separate layers, providing direct adhesion energy values. Scratch tests evaluate interfacial toughness by inducing controlled delamination with a stylus. DCB experiments, on the other hand, are ideal for measuring mode I fracture energy. Data from these tests can refine CZM or J-integral parameters, ensuring model accuracy.

Practical implications of these models include optimizing electrode architecture and material selection. For example, increasing binder content may improve adhesion but reduce energy density. Alternatively, using functionalized binders or surface treatments can enhance interfacial strength without sacrificing performance. Models can also guide manufacturing processes, such as selecting optimal calendering pressure or drying conditions to minimize residual stresses.

In summary, stress-induced delamination in multilayer electrodes is a complex interplay of material properties, interfacial adhesion, and mechanical loading. Cohesive zone modeling and J-integral analysis provide robust frameworks for predicting and mitigating this failure mode. By integrating these models with experimental validation, researchers and engineers can design more durable battery electrodes, ultimately improving performance and longevity. Future work should explore the effects of novel materials and advanced manufacturing techniques on interfacial mechanics, further advancing the field.