Influence of the C-Rate on the Electrolyte Motion Induced Salt Inhomogeneity (EMSI) Effect in a Commercially Available 18650 Lithium-Ion Battery Cell

In recent years, the electrolyte motion induced salt inhomogeneity (EMSI) effect has attracted lots of interest due to its high relevance for the aging behavior of large format lithium-ion cells. In this study, we show that the EMSI effect also occurs in the 18650-type SDI 35E cell, the first demonstration of the EMSI effect in a publicly available commercial lithium-ion cell. The EMSI-specific conducting salt concentration gradient between jelly roll edge and axial-mid plane is measured as a function of cycle number for various C-rates ranging from 0.1 C to 0.9 C. The salt gradient develops within the first 50 to 100 cycles and reaches a steady state thereafter. The magnitude of the steady state salt gradient increases with increasing C-rate. The stabilization of the salt gradient after 50 to 100 cycles has important implications for the interplay of the EMSI effect, C-rate and cell aging which is discussed in detail. In addition, we present a simple analytical technique for the determination of the salt concentration which can be carried out in every electrochemical laboratory without need for special analytical equipment.