Influences of Additives on the Formation of a Solid Electrolyte Interphase on MnO Electrode Studied by Atomic Force Microscopy and Force Spectroscopy

The solid electrolyte interphase (SEI) that forms on electrodes largely defines the performances of lithium ion batteries (LIBs), such as cycling performance, shelf life, and safety. Additives in the electrolyte can modify the properties of the SEI and thus efficiently improve the performances of LIBs. However, the effects of additives on the mechanical properties, structure, and stability of the SEI have rarely been studied directly. In this paper, we report the influence of vinylene carbonate (VC) and lithium bis(oxalate)borate (LiBOB) additives on the mechanical properties of SEI films formed on MnO electrodes using atomic force microscopy (AFM) and force spectroscopy. The results show that the SEI formed from VC additive is thick and soft and partially decomposes upon charging. LiBOB forms thin, stiff, and electrochemically stable SEI films, but the stiff SEI may not be favorable for adapting the volume change of the electrodes. The VC and LiBOB mixed additive combines the advantages of the two components and produces stable SEI with moderate thickness and stiffness. This work also demonstrates that the AFM-force spectroscopy method is effective in investigating the structure and mechanical properties of SEI films.