L’appel du vide: attraction of mobile ions to a polymer-vapor interface

Solid polymer electrolytes are used in many electrochemical devices. While they typically exhibit lower conductivities than liquid electrolytes, they often offer many advantages: longer lasting, higher mechanical strength, and can be solvent-free. However, solid polymer electrolytes are also susceptible to delamination, wherein the electrolyte separates from the electrode, creating voids between it and the electrolyte and thus hindering the performance of the device. This study uses molecular dynamics simulations to characterize structural changes that occur in a system of polyethylene oxide containing aqueous lithium bis(trifluoromethanesulfonyl)imide when it is exposed to a vapor interface. We show that over time the electrolyte and water aggregated at the interface, while the polymer receded toward the center of the condensed phase region. These results indicate that a device undergoing delamination may experience a more catastrophic failure than previously thought.