The Effect of Mechanical Cycling Rate, Operating Temperature, and Solvent on the Mechanics and Electronic Resistivity of Composite Electrodes

Volume changes of the active material lead to a cyclic mechanical loading of composite electrodes during operation. Active material particles and the binder mechanically interact, resulting in an evolution of the structure of the electrode. Here, we mechanically test electrodes in a cyclic compression experiment and measure their strain and resistance under conditions close to application. We investigate the effect of temperature, rate, and the presence of an electrolyte solvent on the electrode dimensions/mechanics and resistivity. We further compare the pure polymeric binder material with composite electrodes to study how the binder affects the electrode mechanics. The results demonstrate that under application conditions electrodes are even less stable and more dynamic than dry model systems. Their viscous, time-dependent mechanical behavior originates from the binder itself and is strongly affected by the presence of the electrolyte solvent, which strongly reduces the stiffness and enhances the flow of the binder. During mechanical loading and unloading, the structure of the composite evolves over the course of several cycles and adapts to the prevailing operating conditions. The properties of battery electrodes, e.g., their dimensions and their resistance, strongly depend on the state of charge, but also on their history of cycling and mechanical load.