The drive to identify high energy batteries remains an on-going challenge. There are two key R & D thrusts at this time – next generation Lithium-ion batteries that (i) require the use of intercalation materials that can operate high voltages (5 V vs Li|Li⁺) and (ii) alternative high energy density electrodes such as Sulfur (2567 Wh/kg) or the holy-grail for the field, an air breathing cathode (3505 Wh/kg). To harness these high energy densities Lithium metal anodes are required as one of very few alternatives. In both instances, there is a distinct need to develop electrolytes that are stable under strongly oxidising environments and strongly reductive environments, respectively.

To this end, CSIRO has been actively researching ionic liquid electrolytes as an option to replace aprotic solvent based electrolytes in batteries. Ionic liquids have some unique properties in terms of negligible vapor pressure, relatively high conductivity, wide electrochemical windows and high thermal decomposition temperatures. This makes them ideally suited to a range of electrochemical storage devices, specifically those that are being targeted at this time.

(i) High voltage lithium-ion batteries require electrolytes that are stable in contact with intercalation cathode at potentials > 4.5 V (vs Li|Li⁺) and do not cause Al current collector corrosion. To-date, there are very few materials that can achieve both of these goals. We will describe work we have been undertaking to determine failure modes of both active materials and electrode structures and the role of the electrolyte in solving these issues.

(ii) Although a 10 fold increase in specific energy is possible with recent advances in Li-Sulfur (2567 Wh / kg) technologies, there are several challenges in the development of these devices. The most vexing of these challenges is the generation of lithium polysulfides which are highly prone to irreversibly move into the electrolyte media. These can have deleterious effects on the performance of the device such as reduced capacity and cycle-life. To overcome this problem, numerous different approaches have been trialled to “lock” S within a conductive structure / matrix whilst still making it available to lithium ions from the electrolyte to form the required lithium polysulfides that deliver the high capacity of the device.

At CSIRO, we have been looking at a range of different methodologies to understand the formation of polysulfides both in the electrolyte and the cathode and then examine various methods to keep them electrically connected within the cathode. In this presentation, we will highlight our work methods to prevent polysulfide dissolution via changes to the electrolyte and the effect on cycling and in-situ studies at the Australian Synchrotron.