Characterization and Prediction of Polymer/Active Material Interface Failure in Battery Electrodes

Background: Failure of polymer/active material interfaces, in commercial composite electrodes, is one of the mechanisms by which batteries loose capacity. In spite of the importance, no systematic study to characterize and understand the interface failure behavior of battery electrodes exists at present. Objective: The objective is to develop an experimental method to characterize the fracture behavior of polymer/active material interfaces in rechargeable battery systems. Methods: Axisymmetric blister test samples were prepared by depositing PVdF (polyvinylidene fluoride) polymer on SiO₂ surface with a series of nanofabrication processes. The PVdF/SiO₂ samples were then pressurized in a novel electrochemical cell until the film delaminated from SiO₂. The mechanical response of the pressurized film was measured, and the PVdF/SiO₂ interface fracture was characterized in terms of critical energy release rate G_c. The fracture surfaces were analyzed to determine failure mechanism. Results: The X-ray photoelectron spectroscopy and scanning electron microscopy analysis of the fracture surfaces showed that the crack path was predominantly at the PVdF/SiO₂ interface, i.e., the mechanism of failure was adhesive. Hence, the measured G_c = 2.46 J/m² can be considered as the energy required to break the bonds to separate PVdF from SiO₂. Using this G_c value in a finite element model, the failure pressure of plane strain blister samples has been predicted successfully. Conclusion: We have experimentally demonstrated that G_c is a fundamental fracture parameter, and G = G_c as a failure criterion can be used to predict PVdF/SiO₂ interface failure irrespective of sample geometry, which can be extended to battery electrodes.