New solid-state materials for energy storage devices are investigated due to their potential to achieve, for example, high reliability and safety as well as high energy density. Of the numerous battery chemistries possible, lithium-ion has become one of the most common technologies for portable electronics and is increasingly employed in electric vehicles and stationary storage.

We have investigated a range of pyrrolidinium and phosphonium based organic ionic plastic crystals (OIPCs), made entirely of ions, that can be applied as attractive, high safety, solid-state electrolytes for lithium batteries.[1,2] These materials offer attractive stable electrolyte properties and unique interfacial properties,[3] key to the use of high energy density electrodes such as lithium metal. Inherently, OIPCs allow flexibility of design and improve safety due to their advantages as non-volatile components of solid-state devices.

In general, the ionic conductivity of OIPCs has been too low for application at ambient temperatures. This presentation will provide an overview of the progress of these materials towards their use in practical solid-state lithium (and sodium) based batteries, including the use of nanoscale polymer composites and the complex role of phase behaviour with addition of lithium and sodium salts.[4-6] Solid-state Li metal | LFP and Li metal | NMC cells with excellent stability and ambient temperature operation are also described.[6,7]

References:

1. MacFarlane, D. R., Meakin, P., Sun, J., Amini, N. & Forsyth M., Pyrrolidinium Imides: A New Family of Molten Salts and Conductive Plastic Crystal Phases, Phys. Chem. B, 103, 4164 (1999).
2. Jin, L., Howlett, P. C., Pringle, J. M., Janikowski, J., Armand, M., MacFarlane, D. R. & Forsyth, M. An organic ionic plastic crystal electrolyte for rate capability and stability of ambient temperature lithium batteries. Energy Environ. Sci. 7, 3352 (2014).
3. Howlett, P. C., Shekibi, Y., MacFarlane, D. R. & Forsyth M., Li-Metal Symmetrical Cell Studies Using Ionic Organic Plastic Crystal Electrolyte, Eng. Mater., 11, 1044 (2009).
4. Howlett, P. C., Ponzio, F., Fang, J., Lin, T., Jin, L., Iranipour, N. & Efthimiadis, Thin and Flexible Solid-State Organic Ionic Plastic Crystal-Polymer Nanofibre Composite Electrolytes for Device Applications. Chem. Chem. Phys. 15, 13784 (2013).
5. Iranipour, N., Gunzelmann, D. J., Seeber, A., Vongsvivut, J., Doherty, C., Ponzio, F., O’Dell, L. A., Hollenkamp, A. F., Forsyth, M., Howlett, P. C., Ionic Transport Through a Composite Structure of N-ethyl-N-methylpyrrolidinium tetrafluoroborate Organic Ionic Plastic Crystals Reinforced with Polymer Nanofibres. Mater. Chem. A. 3, 6038 (2015).
6. Zhou, Y.; Wang, X.; Zhu, H.; Armand, M.; Forsyth, M.; Greene, G. W.; Pringle, J. M.; Howlett, P. C. N-Ethyl-N-Methylpyrrolidinium Bis(Fluorosulfonyl)Imide-Electrospun Polyvinylidene Fluoride Composite Electrolytes: Characterization and Lithium Cell Studies. Chem. Chem. Phys., 19, 2225 (2017).
7. Wang, X.; Zhu, H.; Greene, G. W.; Zhou, Y.; Yoshizawa-Fujita, M.; Miyachi, Y.; Armand, M.; Forsyth, M.; Pringle, J. M.; Howlett, P. C. Organic Ionic Plastic Crystal-Based Composite Electrolyte with Surface Enhanced Ion Transport and Its Use in All-Solid-State Lithium Batteries. Mater. Technol. 8, 1700046 (2017).