Asymmetric Volume Expansion of the Lithium Metal Electrode in Symmetric Lithium/Lithium Cells under Lean Electrolyte and High Areal Capacity Conditions

Abstract

It is known that the quantity of electrolyte significantly impacts cell performance and degradation behavior. Morphological observations of cycled Li/Li symmetric pouch cells under lean electrolyte and high areal capacity conditions are performed using scanning electron microscopy (SEM) and X-ray computed tomography (X-ray CT). Two types of electrolytes, namely, conventional-concentration and high-concentration electrolytes, are applied to the pouch cells. The morphological evolution of the lithium metal electrodes during the dissolution/deposition cycles is successfully characterized from the surface/cross-sectional SEM images, and slice images are constructed using X-ray CT analysis. The slice images show changes in the total cell thickness, and the thickness of the lithium metal electrodes is quantified. The thicknesses of the Li deposits between both sides of the lithium metal electrodes using the conventional-concentration electrolyte clearly show significant asymmetry, suggesting that the subsequent deposition behavior may depend on the initial dissolution and deposition conditions. This study is beneficial for the analysis of next-generation secondary batteries with practical conditions.