Effect of Li⁺ and Mg²⁺ on the Electrochemical Decomposition of the Ionic Liquid 1‐Butyl‐1‐ methylpyrrolidinium bis(trifluoromethanesulfonyl)imide and Related Electrolytes

Abstract

Abstract We investigated the decomposition of 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP‐TFSI) based electrolytes on Au and glassy carbon (GC) in the absence and presence of Li(TFSI) and Mg(TFSI) 2 . Detecting the volatile reaction products via differential electrochemical mass spectrometry (DEMS) measurements allowed us to gain insight into the decomposition mechanisms. In neat ionic liquid (IL) and on Au electrodes both ions are decomposed at reductive potentials. The TFSI − anion mainly decomposes by releasing CF 3 , while for the BMP + cation ring opening and scission of either the methyl or the butyl side chain occur in parallel. At oxidative potentials the decomposition of the anion is the predominant process. Changing to the GC electrode increases the fraction of TFSI − decomposition products at both cathodic and anodic potentials. The addition of Li + largely hinders the formation of volatile BMP‐TFSI decomposition. In contrast, addition of Mg 2+ promotes the TFSI − decomposition at the expense of the BMP + decomposition.