Tailoring oxygen redox reactions in ionic liquid based Li/O₂ batteries by means of the Li⁺ dopant concentration

Abstract

a Ionic liquids' (ILs) reusability, non-volatility and non-corrosiveness, as well as their ease of isolation and a large electrochemical stability window make them an interesting choice as environment-friendly electrolyte for metal/air batteries. ILs have been described as designer solvents as their properties and behaviour can be adjusted to suit an individual reaction need. In the framework of this study we applied a conceptually similar designer approach and show that a simple parameter as the concentration of a Li + dopant dramatically affects the reactions yields of Li/O2 based energy storage devices. We studied the effect of Li + concentration from 0.1 to 1 M in a LiTFSI:PYR14TFSI ionic liquid electrolyte on the kinetics of the oxygen reduction reaction (ORR) and on the formation rate of different Li-O species at two different temperatures, finding that discharge capacity, rates and product distribution change in a non-linear way. At 60 °C highest rates and up to one order of magnitude larger capacities were observed at intermediate LiTFSI concentrations, implying a complete mechanism switch from surface to volume phase mediation for Li2O2 precipitation. At room temperature the same evolution was observed, even if in this case the surface mediation remained predominant at all concentrations. These results suggest the possibility to optimise the ionic liquid based Li/O2 battery performances in terms of discharge capacity and lithium use, by playing on temperature and alkali cation concentration.

Combined Influence of Meso- and Macroporosity of Soft-Hard Templated Carbon Electrodes on the Performance of Li-O2 Cells with Different Configurations

“…In effect, we have shown that the discharge mechanism and the consequent morphology of the deposits is a major factor to consider before determining an optimal electrode architecture [11]. Factors like current density [12,13,14,15,16], electrolyte [17,18,19,20], and cell design [11] can significantly determine whether a surface Li 2 O 2 film forms or larger particles grow from the solution phase. When a 5–10 nm film forms, the ideal pore diameter is twice this thickness, for which pores between 20–40 nm are optimal [21].…”

Porous polyetherimide separators controlled in‐situ by tetrabutyl titanate as polymer electrolyte with ionic liquid for lithium‐oxygen batteries

“…40 Moreover, by adjusting the Li + concentration and the temperature of the ionic liquid electrolytes, the surfacemediated Li 2 O 2 growth mechanism can be transformed into the solution-phase, thereby improving the cycle stability of the lithium-oxygen batteries. 41,42 In this work, using the non-solvent-induced phase separation (NIPS) method, we prepared a PEI-based polymer separator with high porosity, high thermal and chemical stability. During the separator formation process, the in-situ hydrolysis reaction of tetrabutyl titanate (TBT) can not only precisely control the pore structure of the PEI-based polymer separator, but also realize the uniform dispersion of nano-TiO 2 in the polymer matrix.…”