Scanning electron microscopy (SEM) for the electrode reaction in next-generation battery with ionic liquid (IL) electrolyte, which has both high stability under vacuum and an antistatic nature, is applied to the binder-free high capacity Si anode to observe the morphology change of the Si nanoparticle aggregate active material at different potentials during charge-discharge processes. In the IL electrolyte, 1-ethyl-3-methylimidazolium bis(fluoromethylsulfonyl) amide ([C(2)mim][FSA]) with 1.0 M lithium bis(trifluoromethanesulfonyl) amide (Li[TFSA]), the morphology greatly varied at the plateau observed at 0.200 to 0.070 V (vs. Li(I)/Li) in the charge-discharge curve during the first cycle, suggesting that phase transition of a-Si to c-Li13Si4 is a potential problematic process. After the first cycle, the lithiation process initiated at more positive potential. Similar behavior was also recognized in the Li[TFSA]-tetraglyme solvate IL electrolyte in a 1:1 molar ratio ([Li(G4)][TFSA]). (C) 2019 Published by Elsevier Ltd.