2, General Motors Global R&D Center, Warren, Michigan, United States
The potential advantages of lithium (Li) metal anodes have been widely touted (lowest reduction potential, etc.). However, the poor stability of Li metal / liquid electrolyte interfaces leads to chronic problems, such as dendrite formation and capacity loss. The possible impact of mechanical effects on interface stability and dendrite formation leads to critical questions that are difficult to probe directly. An important part of this are the stresses that arise during battery cycling. These were measured with in-situ wafer curvature. Using this technique during Li plating and examining film thickness effects, it was possible to separate contributions from the bulk lithium metal and the solid electrolyte interphase (SEI). These investigations show that significant stresses are created in the SEI films. Similar stress evolution measurements were also performed during lithium plating and stripping using both soft (PEO) and hard (LiF) artificial surface layers. The results indicate that stresses in surface films can be tuned to improve performance when artificial SEI layers are employed. A basic chemo-mechanical model indicates that hybridizing the two layers may benefit interface stability and performance in Li metal anodes.