Failure mechanisms at the Li anode/solid electrolyte interface during Li stripping

Abstract

A precipitous increase in the resistance of the Li metal/solid electrolyte interface can occur during the stripping of Li from the electrode. This electrical failure has been typically attributed to the loss of contact associated with the growth of voids in the Li anode at the electrode/electrolyte interface. We first analyse the growth of voids at the electrode/electrolyte interface using a framework that couples the power-law creep deformation of the Li electrode and the flux of Li+ through a single-ion conductor solid electrolyte. We show that a modified Butler-Volmer kinetics where the local interfacial resistance decreases due to dislocations within the creeping Li predicts that voids indeed grow around interfacial sub-micron impurity particles. Consistent with observations that the increase in resistance of interface occurs earlier for thinner electrodes, we predict that the propensity of void growth increases with decreasing electrode thickness, and this is associated with the mechanical constraint imposed by the current collector. However, in contrast to the observations and rather counterintuitively, this analysis predicts that the cell voltage decreases with void growth. Consequently, we investigate an alternative mechanism of contact loss due to the deposition of insulating solute atoms within the Li electrode onto the interface. Predictions of the rising cell voltage using this analysis are in broad agreement with measurements. This leads us to hypothesize that although void growth occurs at the interface it is not the primary mechanism leading to the increase in interface resistance during stripping.