Ionic Liquid and Plastic Crystal Battery Electrolytes Utilising New Cation and Anion Structures

It is well known that the nature of the cations and anions used to make ionic liquid (IL) electrolytes can have a significant impact on their chemical and physical properties and on their performance in devices, for example when used in lithium or sodium batteries. The same is true for organic ionic plastic crystals (OIPCs); these salts are structurally analogous to ILs, but they are solid at room temperature and display dynamics that can allow their use as solid state electrolytes. However, the structure-property relationships are arguably even less well understood in OIPCs. Furthermore, the addition of different lithium or sodium salts to ILs and OIPCs, to enable their use in lithium or sodium batteries, introduces further complexities in terms of understanding and optimising the thermal, electrochemical and transport properties. To advance the understanding and application of IL and OIPC-based electrolytes it is important to continue to design and investigate new cation and anion structures. For example, we have recently developed new families of IL and OIPC electrolytes using cations such as the hexamethylguanidinium, cyano- or ether-functionalised ammoniums, oxazolidiniums and morpholiniums, in combination with a range of fluorinated and non-fluorinated anions. Furthermore, a new and seldom explored family of materials can be created by tethering the cation and anion together to form zwitterions. This presentation will give an overview of our recent work making new families of non-volatile electrolytes based on ILs, OIPCs and zwitterions and understanding the impact of structure on device performance. Highlights will include the excellent properties and performance imparted by small oxygen-containing cations, and the promising new results using more environmentally friendly, non-fluorinated salts for Li and Na batteries. References [1] A. Warrington, M. Hasanpoor, A. Balkis, P. C. Howlett, O. E. Hutt, M. Forsyth, J. M. Pringle, Energy Storage Materials 2023, 63, 102984 [2] A. Sourjah, C. S. M. Kang, C. M. Doherty, D. Acharya, L. A. O’Dell, J. M. Pringle, Phys. Chem. Chem. Phys., 2023, 25, 16469 [3] F. Makhlooghiazad, L. A. O’Dell, L. Porcarelli, C. Forsyth, N. Quazi, M. Asadi, O. Hutt, D. Mecerreyes, M. Forsyth, J. M. Pringle, Nat. Mater., 2022, 21, 228