Effect of Surface Nature on Stripping of in Situ li Anodes and Enhancement of Its Stripping Capacity

Abstract

Li-metal solid-state batteries (LMSSBs) have been considered disruptive technologies for the widespread adoption of EVs due to their improved safety and higher energy density. Recently, in situ Li anode formation on solid-electrolytes (SEs) has garnered interest owing to its low manufacturing cost, high purity, and enhanced energy density. Thus, there have been intense efforts to understand the mechano-electrochemical properties of in situ Li anodes. Our previous work has demonstrated that the accessible capacity of in situ thin Li decreases as current density increases. This result indicates that more Li will remain inaccessible as the stripping rate increases, leading to the reduced energy density of LMSSB cells. To minimize the amount of inaccessible Li at high stripping rates, it is essential to investigate the factors affecting the stripping capacities of in situ Li and devise a new way to achieve enhanced stripping capacities at high stripping rates.First, this study focuses to understand the correlation between the stripping capacity of in situ thin Li and the nature of the surface. This study demonstrates that the nature of the surface can dramatically affect the stripping capacity. When discharging at room temperature and 3 mA/cm2, approximately 50% of the accessible capacity of in situ plated Li was achieved.Furthermore, this study demonstrates that stripping Li under conditions that more closely resemble an EV duty cycle improves the accessible capacities at high stripping rates. By introducing short intermittent rest periods during stripping, the Li/LLZO interface can be relaxed as Li vacancies at the interface can be moved away, preventing voids to forms. Also, even if voids form at the interface, the growth of voids can be delayed because of rewetting mechanisms during the rest periods.This study is expected to not only provide insight into the stripping properties of in situ Li, but also suggest future guidelines for the practical discharge protocols of anode-free LMSSBs with commercially-relevant discharge rates.