Thermodynamic Effect of Anion Activity on Electrochemical Reactions Involving Li + Ions in Room‐Temperature Ionic Liquids

The effect of Li + concentration on the electrochemical reactions of Li metal and graphite electrodes was studied in aprotic ionic liquid (P13TFSA: N ‐methyl‐ N ‐propylpyrrolidinium bis(trifluoromethanesulfonyl)amide)‐LiTFSA mixtures. The electrode potential of the Li metal was governed not only by the activity of the complex Li + ions ([Li(TFSA) 2 ] − ), but also by the free‐TFSA − anions, because the desolvation step of the complex Li + ions needed to be considered. With increasing LiTFSA concentration, the electrode potential of the Li metal increased due to increasing [Li(TFSA) 2 ] − activity and decreasing free‐TFSA − activity in the electrolyte solutions, which was supported by Raman spectroscopy results. The Li + intercalation reaction into the graphite electrode was also investigated. With increasing LiTFSA concentration, the onium cation (P13 + ) intercalation, which is a well‐known side reaction without a desolvation step, was suppressed and reversible Li + intercalation into the graphite electrode was observed.