Mechanical Evolution of Solid Electrolyte Interphase on Metallic Lithium Studied by in situ Atomic Force Microscopy

Metallic lithium is a promising candidate as anode material in lithium batteries due to its high specific capacity and cell voltage. However, the high reactivity of metallic lithium leads to a rapid formation of the solid electrolyte interphase (SEI), even without an applied voltage. Unfortunately, the formation mechanism of the SEI is not yet fully understood. An exact understanding of the SEI includes mechanical properties, such as stiffness. Here, the mechanical properties during SEI formation are studied in an electrolyte consisting of 1.2 M LiPF 6 in a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) without applied potential using in situ atomic force microscopy (AFM). The formation of the SEI is investigated by mapping the mechanical evolution of the surface. Thereby, changes of surface composition are visualised over time. Moreover, for the addition of vinylene carbonate as an additive to the electrolyte, the impact on the morphology as well as the stiffness is demonstrated.