New crystals show promise as safer electrolytes

Organic ionic plastic crystals (OIPCs) and ionic liquids (ILs) are promising safer electrolytes for energy storage applications.

OIPCs are a type of solid-state electrolyte composed entirely of ions with the advantageous properties observed in ILs such as non-flammability, high conductivity and the ability to form stable and highly conductive solid electrolyte interface layers in lithium cells.

The library of cations known to form OIPCs is quite small and the development of new cations is critical to advance their use as solid electrolytes. storEnergy PhD student Anna Warrington has synthesised a new cation with the aim of creating new OIPCs for battery electrolyte applications.

The structure of the cations and anions has a big effect on the crystal properties, such as thermal behaviour and ionic conductivity.

Synthesising new cations is not an easy task and Anna worked closely with a team of experienced synthetic chemists at storEnergy industry partner, Boron Molecular.

“I think trying to be creative when designing these cations is important and can help change their properties a lot,” she says.

After synthesising the cation, Anna paired them with different anions known for their suitability for electrochemical applications, to form salts. Of the six salts synthesised, only three formed crystals, one formed an ionic liquid and two formed high-melting ionic liquids.

These new OIPCs expand the library of potential solid-state and liquid electrolytes, not only for alkali metal battery applications but also in applications such as CO₂ capture, gas separation, solid-state supercapacitors and as potential binders in electrode materials.

“OIPCs can be unpredictable and by making a large number of different ones we hope to be able to start better predicting their properties,” explains Anna.

She is focusing on one OIPC in particular, which is very thermally stable, and due to the oxygen-functionality on the cation has enhanced conductivity and ion dynamics. To test how the material performs as an electrolyte, she is dissolving Li salt into it and testing how it behaves in a lithium metal battery.

Boron Molecular Business Development Manager, Dr Joshua Boyle said the development of new electrolytes is an exciting prospect, and Boron Molecular is thrilled to be involved through its partnership with Deakin University through the storEnergy collaboration.

“This collaboration is a win-win situation for both partners, as Boron Molecular gets access to the extensive battery expertise that is present at Deakin University, while Anna and her colleagues get to experience the fast-paced nature of working in an industrial lab and the benefits and challenges that go with that,” says Dr Boyle.

In future, Anna would like to keep working on developing new materials for battery applications. “More and more companies are realising that they need to start making their own batteries. It’s an exciting time to be involved in the industry,” she says.

Reference: Thermal, structural and dynamic properties of ionic liquids and organic ionic plastic crystals with a small ether-functionalised cation. Warrington, A., Kang, C.S.M., Forsyth, C., Doherty, C.M., Acharya, D., O’Dell, L.A., Sirigiri, N., Boyle, J.W., Hutt, O.E., Forsyth, M., Pringle, J.M. Materials Chemistry Frontiers 2022