We report an in situ scanning tunneling microscopic study of surface morphology changes in Au（111） electrode in 1-ethyl-3-methylimidazolium bis（trifluoromethylsulfonyl）imide （EMITFSI） ionic liq- uid containing LiTFSI salt. The surface processes can be divided into three stages： In the first stage, a re- duction wave of dissolved oxygen in the ionic liquid appears at approximately 2.0 V and a network structure covers the surface afterward; in the second stage at around 1.5 V, reduction of trace water is initiated and a surface film containing lithium hydroxide is formed; in the third stage, as potential is further decreased to 0.85 V, decomposition of the EMITFSI ionic liquid occurs, which is accompanied by lithium underpotential deposition and Au-Li alloying. In this stage, the surface experiences significant morphological changes with formation of many clusters on the surface, and even- tually becomes electronically less conductive. This unique surface film is understood to be the initial stage formation of a solid electrolyte interphase on gold, which may be a common feature in ionic liquids in the presence of lithium salt.
