Ionic Liquid Electrolytes – from Novel Separators to Solid Polymer Electrolytes

Abstract

One of the significant challenges to the application of ionic liquid electrolytes (ILE’s) is the ability to identify separators that can be effectively ‘wetted’ by the electrolyte. There has been significant work in identifying appropriate commercial separators for these electrolytes, with varying degrees of success [1]. To-date, the most effective separator for ILE’s is glass fibre, however, this material has large, open pore structure and this requires it to relatively thick to prevent short circuits between the electrodes. As a consequence, there is a need to identify new materials / structures that can lead to innovative separators that can allow ILE’s to be effectively used in batteries. To this end, we have examined the use of a “supported” electrospun membrane to be able to “tailor” the interfaces of the electrodes, but also allow effective wetting of the separator with an ILE to enable use in a lithium-ion battery [1]. However, in doing this, we have now made a “simple” separator far more complex in order to address the ILE wetting problem. So the question needs to be asked – can we combine the properties of the complex separator with an ILE into one solution, such as a solid polymer electrolyte? Further, can we improve these materials by exploiting micro-phase structured morphologies to provide us with enhanced mechanical properties as well? One type of these micro-phase structured polymers [2], known as PILBlox, is made of a high T g block for mechanical strength and a low T g ionic block for ionic conductivity [3, 4]. Combining PILBlox with a lithium based ionic salt and an ionic liquid forms a polymer electrolyte which ideally maintains the micro-phase separation present of the pure PILBlox polymer, and confines the ionic salt and ionic liquid to the ionic block of the polymer [4, 5]. In this presentation, we will describe our efforts to make innovative separators using electrospinning techniques and the resulting electrochemistry, before turning our attention to the PILBlox materials and examining their physical properties and their potential use in solid state batteries. References Francis. C., et al., manuscript in preparation, 2018. Bates, F.S., Polymer-Polymer Phase-Behavior. Science, 1991. 251 (4996): p. 898-905. Dean, J.M., et al., Micellar structure and mechanical properties of block copolymer-modified epoxies. Journal of Polymer Science Part B-Polymer Physics, 2001. 39 (23): p. 2996-3010. Nykaza, J.R., et al., Polymerized ionic liquid diblock copolymer as solid-state electrolyte and separator in lithium-ion battery. Polymer, 2016. 101 : p. 311-318. Meek, K.M. and Y.A. Elabd, Polymerized ionic liquid block copolymers for electrochemical energy. Journal of Materials Chemistry A, 2015. 3 (48): p. 24187-24194.