Characterization of Lithium Inventory in Lithium Metal Anodes during Cycling

Abstract

A rising interest in batteries has resulted from a need for improved energy storage systems for transportation and portable electronics applications. Lithium is of particular interest as an anode due to its low redox potential and high specific capacity. However, these systems have not been practically realized due to the nonuniform plating of lithium. Many studies have modeled this formation of dendritic or mossy structures as a function of parameters such as temperature, electrolyte composition, current density and overpotentials [1]. However, the majority of these efforts have focused on the influence of these parameters on the nucleation and growth of lithium at early stages; the processes for deplating of lithium during discharge and the continued growth of dendritic structures, once formed, are poorly understood. In this work, we use commercially available primary cells as a basis for understanding the movement of lithium during cycling. Specifically, we discharge both coin and pouch cells at a range of C rates to specified states of charge (SOC). During discharge, acoustic time of flight studies are used to provide insight on how mass is transferred between layers [2]. Once the cell has been discharged to the specified SOC, electrochemical impedance spectroscopy is conducted before dismantling the cell and observing the lithium electrode using scanning electron microscopy. The same characterization methods are subsequently used for cells that have been discharged and charged for a range of cycles. Through these techniques, we track how lithium is transferred between electrodes, as well as how lithium is spatially utilized across the anode.