We analyze the effects of mechanical stresses arising in a solid polymer electrolyte (SPE) on the electrochemical performance of the electrolyte component of a lithium ion battery. The SPE is modeled with a coupled ionic conduction-deformation model that allows to investigate the effect of mechanical stresses induced by the redistribution of ions. The analytical solution is determined for a uniform planar cell operating under galvanostatic conditions with and without externally induced deformations. The roles of the polymer stiffness, internally-induced stresses, and thickness of the SPE layer are investigated. The results show that the predictions of the coupled model can strongly deviate from those obtained with an electrochemical model—up to +38% in terms of electrostatic potential difference across the electrolyte layer—depending on the combination of material properties and geometrical features. The predicted stress level in the SPE is considerable as it exceeds the threshold experimentally detected for irreversible deformation or fracture to occur in cells not subjected to external loading. We show that stresses induced by external solicitations can reduce the concentration gradient of ions across the electrolyte thickness and prevent salt depletion at the electrode-electrolyte interface.@en

We study the effect of mechanical stresses arising in solid polymer electrolytes (SPEs) on the electrochemical performance of lithium-ion (Li-ion) solid-state batteries. Time-dependent finite element analyses of interdigitated plate cells during a discharge process are performed with a constitutive model that couples ionic conduction within the SPE with its deformation field. Due to the coupled nature of the processes taking place in the SPE, the non-uniform ionic concentration profiles that develop during the discharge process induce stresses and deformations within the SPE; at the same time the mechanical loads applied to the cell affect the charge conduction path. Results of a parametric study show that stresses induced by ionic redistribution favor ionic transport and enhance cell conductivity—up to a 15% increase compared to the solution obtained with a purely electrochemical model. We observe that, when the contribution of the mechanical stresses is included in the simulations, the localization of the electric current density at the top of the electrode plates is more pronounced compared to the purely electrochemical model. This suggests that electrode utilization, a limiting factor for the design of three-dimensional battery architectures, depends on the stress field that develops in the SPE. The stress level is indeed significant, and mechanical failure of the polymer might occur during service.@en