Indentation elastic work recovery: A mechanical index of solid electrolyte interphase for effectively assessing electrochemical properties of lithium metal anode

Lithium metal anode has attracted wide attention due to its high theoretical specific capacity (3860 mAh g-1) and other advantages. The main bottleneck of lithium metal anode stems from the deterioration and failure of solid electrolyte interphase (SEI). The mechanical properties of SEI have been widely acknowledged as an important factor in evaluating the cycling stability. However, there is a scarcity of studies on the relationship between the mechanical properties of SEI and electrochemical properties, as well as a lack of an appropriate mechanical index for roundly evaluating the ability of SEI to resist deformation and fracture. In this study, the mechanical properties of the SEI are measured by nanoindentation and an index of "elastic work recovery (We/ Wt)" is constructed to evaluate. Based on this method, we investigate the SEIs prefabricated under two electrolytes, five current densities and five capacity densities, which demonstrates a consistent correlation between elastic work recovery of the SEIs and the electrochemical properties. Moreover, the easily obtained elastic work recovery index is higher sensitive compared to the conventionally used modulus index. This study will not only enhance the understanding in the mechanical role of SEI films but also provide an effective means for evaluation.