Molecular Dynamics Simulations of the Traction-Separation Response at the Interface between PVDF Binder and Graphite in the Electrode of Li-Ion Batteries

Fracture in Li-ion battery electrodes is one of the main degradation mechanisms that limit the battery performance and lifetime. Debonding between the active and binder materials damages mechanical integrity, which leads to the loss of active materials and increased resistance. In this work, molecular dynamics (MD) simulation is used to evaluate the strength of the connectivity between polyvinylindene fluoride (PVDF) binder and graphite in the opening and sliding modes. The simulations revealed detailed failure behaviors at the atomistic scale. We have found that the separation occurs at the interface rather than inside the bulk materials, suggesting that the mechanical strength at the interface between PVDF binder and graphite is weaker than that of PVDF or graphite. Therefore, debonding at the interface is critical to the mechanical integrity of the electrode. Our calculations have provided quantitative traction-separation curves, and identified the maximum stresses of 300 MPa and 30 MPa for the normal and shear traction curves, respectively. The traction-separation curves obtained from the MD simulations will provide the critical input for the continuum level cohesive zone model to further study the inter-particle crack propagation in the electrode.