Stability of Glyme Solvate Ionic Liquid as an Electrolyte for Rechargeable Li−O₂ Batteries

Abstract

A solvate ionic liquid (SIL) was compared with a conventional organic solvent for the electrolyte of the Li-O battery. An equimolar mixture of triglyme (G3) and lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]), and a G3/Li[TFSA] mixture containing excess glyme were chosen as the SIL and the conventional electrolyte, respectively. Charge behavior and accompanying gas evolution of the two electrolytes was investigated by electrochemical mass spectrometry (ECMS). From the linear sweep voltammetry performed on an as-prepared cell, we demonstrate that the SIL has a higher oxidative stability than the conventional electrolyte and, furthermore, offers the advantage of lower volatility, which would benefit an open-type lithium-O cell design. Moreover, CO evolution during galvanostatic charge was less in the SIL, which implies less side reaction. However, O evolution during charge did not reach the theoretical value in either of the two electrolytes. Several mass spectral fragments were generated during the charge process, which provided evidence for side reactions of glyme-based electrolytes. We further relate the difference in observed discharge product morphology for these electrolytes to the solubility of the superoxide intermediate, determined by rotating ring disk electrode (RRDE) measurements.

Factors influencing fast ion transport in glyme-based electrolytes for rechargeable lithium–air batteries

“…Li salt electrolytes are expected to widen the electrochemical window; i.e., improve electrochemical stability. [19][20][21]32 This is also attractive as an electrolyte property for use in next-generation batteries such as LABs that need a relatively high potential (over 4.2 V) at the air electrode for the charge process. However, conc.…”

“…This trend was similar to those reported for electrolytes for Li-ion batteries (LIBs) 24 and was also in good agreement with those of solvate ionic liquids. 19,20,32 The orders of magnitude of D were LiOTf > LiFSI > LiTFSI and 0.5 M > 1.0 M > 2.0 M > 2.7 M for the type of Li salt and its concentration, respectively. These trends do not correspond to those for s. This indicates that s is strongly inuenced by n in the electrolytes.…”

“…Watanabe et al 19,20 developed concentrated Li salt glymebased electrolytes, called solvate ionic liquids, for LAB and Li-S battery systems. These electrolytes displayed interesting properties such as quite low solubility of polysulde lithium and high electrochemical stability derived from the strong interaction between Li + and glyme (G3, G4) solvents.…”

“…In the glyme electrolytes, the mutual interactions between ions and solvent are relatively strong and inuence the ion transport behavior by changing the solvation structures. As shown by eqn (1), s of solution electrolytes is also inuenced by n. In the following section, we conducted analyses using Walden plots and the Nernst-Einstein equation to elucidate the effect of n on s. 19,20,32 Therefore, the contribution of n to s increases with rising concentration especially at lower temperatures. In contrast, lower Li salt concentration and higher temperature are considered to increase the contribution of m to s.…”

Solvate Ionic Liquids for Li, Na, K, and Mg Batteries

“…The comprehensive investigations based on both experiments and calculations have shown that the formation of stable solvate cations is responsible for the high thermal and enhanced electrochemical stabilities ,,,. SIL‐based electrolytes have also shown excellent performance in various advanced Li‐based batteries ,…”