Tailoring oxygen redox reactions in ionic liquid based Li/O 2 batteries by means of the Li + dopant concentration

CECCHETTO, LAURA; TESIO, ALVARO Y.; OLIVARES-MARÍN, MARA; ESPINASA, MARC GUARDIOLA; CROCE, FAUSTO; TONTI, DINO

Sustainable Energy & Fuels

Royal Society of Chemistry

Lugar: Cambridge; Año: 2018 vol. 2 p. 118 - 124

The reusability, non-volatility and non-corrosiveness of ionic liquids (ILs), as well as their ease of isolationand a large electrochemical stability window, make them an interesting choice as environmentallyfriendly electrolytes for metal/air batteries. ILs have been described as designer solvents as theirproperties and behaviour can be adjusted to suit an individual reaction need. In the framework of thisstudy we applied a conceptually similar design approach and showed that a simple parameter such asthe concentration of a Li+ dopant dramatically affects the reaction yields of Li/O2 based energy storagedevices. We studied the effect of Li+ concentration from 0.1 to 1 M in a LiTFSI:PYR14TFSI ionic liquidelectrolyte on the kinetics of the oxygen reduction reaction (ORR) and on the formation rate of differentLi?O species at two different temperatures, finding that the discharge capacity, rates and productdistribution change in a non-linear way. At 60 C, the highest rates and up to one order of magnitudelarger capacities were observed at intermediate LiTFSI concentrations, implying a complete mechanismswitch from surface to volume phase mediation for Li2O2 precipitation. At room temperature the sameevolution was observed, even if in this case the surface mediation remained predominant at allconcentrations. These results suggest the possibility to optimise the ionic liquid based Li/O2 batteryperformances in terms of discharge capacity and lithium use, by tuning the temperature and alkali cationconcentration.