Investigating Electrolyte Motion in Li-Ion Batteries - A Nodal-Analysis-Based Simulation Framework

Electrolyte motion induced salt inhomogeneity (EMSI) has been suggested as a novel ageing mechanism occurring in lithium-ion batterys (LIBs). Electrolyte motion refers to the movement and flow of electrolyte within LIBs as a result of active material (AM) expansion and contraction during operation. EMSI is suspected to cause capacity loss and the occurrence of in-plane salt concentration gradients in the electrolyte. To depict the mechanism and deepen understanding of its impact on lithium-ion battery (LIB) performance, we present a nodal-analysis-based pseudo-3D simulation framework that allows efficient computation of the interplay between battery operation and electrolyte flow, utilising equivalent circuit model elements. Using the presented framework, we demonstrate that in-plane concentration gradients and extrema form, even in small-format cells. The resulting concentration extrema lead to conductive and kinetic impediments that reduces the state-of-lithiation window in certain electrode areas, causing the capacity loss. Beyond that, we see in the mid-term an accumulation of Li + in the electrolyte and in the long-term an accumulation of Li in the AM toward the axial middle of the cell. In sum, the presented framework demonstrates a convenient approach to depict fluid dynamics of the electrolyte in LIBs, motivating further research on electrolyte motion induced salt inhomogeneity (EMSI) and its consequences.