Stability of a Pyrrolidinium-Based Ionic Liquid in Li-O2 Cells

Abstract

The use of 1-methyl-1-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr14TFSI) electrolyte in different Li-O2 cell setups is here investigated. In a one-compartment Li-O2 cell, the pyrrolidinium ion is reduced on metallic lithium, producing substantial amounts of alkenes and amines. To avoid this, a simple two-compartment cell is used, with propylene carbonate as anode electrolyte and a Li+-ion solid electrolyte as separator. Another explored option is the substitution of lithium in the one-compartment cell with lithiated LTO (LLTO). Unfortunately, the absence of an SEI leads to the reduction of O2 at LLTO, making it not useful as counter electrode for Li-O2 cell evaluation. All the configurations above are characterized by a first discharge specific capacity double than that obtained with unreactive electrolytes. The use of an edge-sealed two-compartment LLTO-Vulcan cell resulted in the usual discharge capacity of ≈200 mAh g−1C at the first cycle, eliminating the effects of Pyr14TFSI reduction; nevertheless, the poor cyclability even in this cell design suggests that Pyr14TFSI might not have sufficient long-term stability against the attack of O2•− during discharge or of oxygen species during charge.