From Mosaic-Type to Heterojunction-Type SEI Films on the Li Anode: Decoupling Chemical and Electrochemical Degradation of the Electrolyte

The solid electrolyte interphase (SEI) film is vital to the plating/stripping behavior of lithium metal, while the formation mechanism has not been explained clearly. Here, the formation process of the SEI film is first classified into chemical and electrochemical degradation routes by introducing a LiZn alloy, a chemically inert but electrochemically reactive interphase, as a distinguished research substrate. In a carbonate electrolyte, it is found that the common inorganic matters (such as Li2O and LiF) mainly originate from the chemical degradation of the electrolyte; meanwhile, the electrochemical degradation mainly generates organic species such as C-OR and COOR. Based on this understanding, the SEI film can be further accurately regulated, and a heterojunction-type SEI film with a well-defined composition and structure is constructed. This offers us a new perspective to understand and regulate the formation of the SEI film for applicable lithium metal batteries.