Quantifying the Evolution of Binder/Active Material Interface Fracture Properties from the As-Prepared State to Cycling Conditions

The binder-active material interface failure has been a critical issue in rechargeable batteries, especially for high-performance materials with large (∼300%) volume changes. This interface is very complex and undergoes various changes over the course of fabrication to cycling in service. Here, PVdF/Si was chosen as a model interface, and the interface failure behavior is quantified in terms of critical energy release rate <i>G</i> _c. Further, the effect of electrolyte and the electrochemical cycling on <i>G</i> _c was quantified using an experimental method, which includes a Michelson interferometer-based optical setup coupled with a blister test in an electrochemical cell. The <i>G</i> _c of the as-prepared dry PVdF/Si interface is 0.55 ± 0.10 J m^-2, but it decreased to 0.31 ± 0.10 J m^-2 (i.e., a 40% reduction) upon introducing the electrolyte. The interface fracture property, <i>G</i> _c, further reduces to 0.26 ± 0.03 J m^-2 (additional 21% decrease) due to subsequent electrochemical cycling. It was also observed that the measured <i>G</i> _c is independent of sample geometry and is only a function of materials that make up the interface. The surface analysis (SEM and XPS) showed that the crack propagation in these samples occurred at the interface (i.e., neither in the PVdF nor in the Si substrate). Therefore, the reduction in <i>G</i> _c is attributed to the changes in the bonding environment at the interface due to electrolyte solvents and subsequent chemical changes that occur at the interface due to electrochemical cycling.