Reactivity of the Ionic Liquid Pyr₁₄TFSI with Superoxide Radicals Generated from KO₂or by Contact of O₂with Li₇Ti₅O₁₂

Abstract

Ionic liquids are attractive candidates as electrolyte solvents for Li-O 2 cells, primarily due to their low volatility, high anodic stability, and low flammability. Specifically, the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr 14 TFSI) has attracted considerable attention thanks to its electrochemical and chemical stability. In this work, we demonstrate via our recently developed UV-Vis screening method that Pyr 14 TFSI unfortunately reacts with the superoxide radical (O •− 2 ) which is produced during the discharge of Li-O 2 cells. To clarify the reaction mechanism of O •− 2 with Pyr 14 TFSI, we take advantage of the recently described formation of O •− 2 upon contact between lithiated lithium titanate (LTO) and O 2 to produce a sufficient amount of degradation products from the reaction of Pyr 14 TFSI with O •− 2 that can be detected by NMR. Furthermore, we validate this new screening method for solvent decomposition by superoxide radicals by investigating the behavior of lithiated LTO in contact with O 2 using RRDE voltammetry.

Why Do Lithium–Oxygen Batteries Fail: Parasitic Chemical Reactions and Their Synergistic Effect

“…[11] In those experiments,H 2 was detected as amajor gas phase byproduct during discharge,pointing to a b-H elimination mechanism by acid-base chemistry.T wo recent studies by the Gasteiger group provided strong evidence to support the decomposition pathways of PYR 14 TFSI (1-butyl-1-methylpyrrolidinium bis-(trifluoromethanesulfonyl)imide) following the Hofmann elimination mechanism. [47,48] As as oft acid, PYR cation interacts favorably with superoxide,w hich is as oft base, according to the half-soft acid-base (HSAB) theory. [49] This interaction helps stabilize superoxide in the electrolyte, promoting OER reactions following ao ne-electron process.…”

“…See Section 2.5 for discussions of the SEI formation and functionality. [31,35] --Ether/polyether -O ,P [20,42,44,51] -O [43] DMSO B, [32] N [30] B, [32] N, [30] P [46] R [19] -Ionic liquid -B [47,48] R [47] -Amide -N [39,40] R [55] -Notes:N:nucleophilic attack;B:acid-base reaction;O:auto-oxidation; P: proton-mediated process;R:r eduction by Li.…”

Warum Lithium‐Sauerstoff‐Batterien versagen: Parasitäre chemische Reaktionen und ihr synergistischer Effekt

“…In diesen Versuchen wurde H 2 als Hauptnebenprodukt in der Gasphase während des Entladens nachgewiesen, was auf einen Mechanismus der β‐H‐Eliminierung über Säure‐Base‐Reaktionen hindeutet. Zwei neuere Studien der Gruppe von Gasteiger erbrachten den eindeutigen Nachweis der Zersetzungswege von 1‐Butyl‐1‐methylpyrrolidiniumbis(trifluormethansulfonyl)imid (PYR 14 TFSI) nach dem Mechanismus der Hofmann‐Eliminierung . Als weiche Säure wechselwirkt das PYR‐Kation gut mit Superoxid, das eine weiche Base ist – gemäß dem Konzept der harten und weichen Säuren und Basen, HSAB‐Konzept (HSAB, Hard and Soft Acids and Bases) .…”

“…Infolgedessen werden nur geringe Überspannungen beim Laden gemessen . Die relativ hohe Konzentration an Superoxid in PYRTFSI fördert jedoch auch die β‐H‐Eliminierung am PYR‐Kation durch das Superoxid, was zur Zersetzung des Elektrolyten führt …”

Investigating the Long-Term Stability and Kinetics of Superoxide Ion in Dimethyl Sulfoxide Containing Ionic Liquids and the Application of Thiophene Destruction

“…Several studies have reported the long-term stability of O2 − with ILs (AlNashef et al, 2010;Hayyan et al, 2012d;Hayyan et al, 2012f) and other electrolytes, such as glyme (Schwenke et al, 2013). Recently, Schwenke et al (2015) monitored O2 − with 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide for 18 h.…”