Meaning
Parallel mechanical force per unit area that acts along the boundary between two contacting solid layers. In composite battery electrodes, this interfacial shear stress arises during cycling as the active materials expand and contract against the rigid current collector or the polymer binder. High values lead to mechanical degradation, including detachment of the active layer from the metal foil.
Delamination Cause
Differential volume changes between the silicon particles and the surrounding matrix create severe strain gradients during charge cycles. This interfacial shear stress exceeds the adhesive strength of the binder, separating the active slurry from the copper foil. Such physical detachment isolates active material from the electrical path, accelerating capacity fade.
Cycling Mechanism
Interfacial shear stress increases when the rate of charge or discharge elevates, since rapid phase transformations generate sharper concentration gradients. Polymeric binders with high elasticity can deform to accommodate these stresses, whereas rigid binders fail and generate microcracks. This mechanical decay limits the power density of thick-electrode designs.
Coating Design
Thin-film surface coatings or functionalized binders reduce the local strain mismatch at the boundaries of the composite electrode. Sourcing decisions for advanced binder chemistries focus on maximizing the shear adhesion to prevent delamination under these mechanical loads. This approach ensures long-term electrochemical stability by preserving the integrity of the solid interface.
Polymer chains that chemically bond to both the metal oxide and the carbon black disperse these local forces across a larger surface area, mitigating the risk of localized mechanical failure during deep discharge cycles.
