Funding: Army Research Laboratory – Materials Center of Excellence (MCOE), Army Research Office – Multidisciplinary University Research Initiative (MURI), Nanotechnology Institute via Ben Franklin Technology Partners
Collaborators: Winey (Univ. Penn.), Long (Va. Tech.), Beyer (ARL)

Solid-state polymer electrolytes with high ionic conductivities have been the subject of extensive research for electrochemical devices, such as fuel cells and batteries. In our laboratory, we are synthesizing and characterizing a new class of solid-state polymer electrolyte: polymerized ionic liquid block copolymers (PILbloX), which combine the benefits of block copolymers and ionic liquid-based chemistry. We are exploring the transport of hydroxide and lithium in this new class of materials for application to alkaline fuel cells and lithium ion batteries.

For alkaline fuel cells (AFCs), chemically stable, mechanically robust, highly hydroxide conductive anion exchange membranes (AEMs) are required as electrolytes to realize high power density, long-lasting AFCs. AFCs are attractive replacements to traditional proton exchange membrane fuel cells, because they do not require the use of expensive precious metal catalysts, but can operate with cheaper non-noble metal catalysts (e.g., Ni) due to their facile electrokinetics in alkaline conditions. Our new PILbloX AEM demonstrates that chemically stable, mechanically robust, highly hydroxide conductive AEMs with new cation chemistries are now possible.

Surprisingly, the hydroxide conductivity of our PILbloX AEM is not only higher (over an order of magnitude) than its random copolymer analog at the same ion and water content, but also higher than its homopolymer analog, which has a higher ion and water content than the block copolymer. This is a product of PILbloX's nanostructured morphology, where nanochannels accelerate hydroxide ion mobility, which should subsequently result in higher power densities in an AFC. These results should have a significant impact on low-cost (platinum-free) long-lasting solid-state AFCs. We are now exploring morphology-transport relationships in PILbloX AEMs under controlled environments (humidity, temperature, voltage) using in situ time-resolved infrared spectroscopy and in situ multi-angle X-ray scattering techniques. This will guide the future synthesis of different PILbloX AEMs with optimal morphology and ion transport. We are also integrating our PILbloX AEMs into AFCs and testing fuel cell performance.

We have also developed lithium ion conducting PILbloX solid-state polymer electrolytes (SPEs) for integration into lithium ion batteries. Currently, high manufacturing costs and concerns about battery safety and stability hinder the market growth of the lithium ion battery. Replacing liquid-based electrolytes in lithium ion batteries with SPEs can alleviate many cost, safety, and stability concerns and is arguably the most attractive new technology for rechargeable electric power sources. However, this will require SPEs with properties of high lithium ion conductivity, excellent mechanical properties, and good processability. Our recent results demonstrate robust and processable PILbloX SPEs with high lithium ion conductivity. These results are a product the nanostructured morphology of our PILbloX, where nanochannels accelerate the lithium ion transport, which should result in faster charge/discharge rates in batteries. The PIL chemistry in PILbloX also allows for a broad electrochemical window (> 6 V) and is non-flammable and non-volatile. The chemistry of these nanochannels (PIL) and nanostructured morphology in our PILbloX are both novel and commercially viable to batteries. We are now exploring transport-morphology-processing relationships to guide the synthesis of new PILbloXs and integrating PILbloX SPEs into coin cells for battery testing.

Selected Publications and Patents:
  1. Elabd, Y.A.; Winey, K.I.; Ye, Yuesheng, Choi, J.-H. Sherick, T.-S. S. Polymerized Ionic Liquid Block Copolymers As Battery, U.S. Patent Application, filed September 12, 2013, Appl. No.: 14/024,734, pending approval.
  2. Ye, Y.; Wang, S.; Davis, E.M.; Winey, K.I.; Elabd Y.A. High Hydroxide Conductivity in Polymerized Ionic Liquid Block Copolymers. ACS Macro Letters 2013, 2, 575-580.
  3. Choi, J.-H.; Ye, Y.; Elabd, Y.A.; Winey, K.I. Network Structure and Strong Microphase Separation for High Ion Conductivity in Polymerized Ionic Liquid Block Copolymers. Macromolecules 2013, 46, 5290-5300.
  4. Ye, Y.; Choi, J.-H.; Winey, K.I.; Elabd, Y.A. Polymerized Ionic Liquid Block and Random Copolymers: Effect of Weak Microphase Separation on Ion Transport. Macromolecules 2012, 45, 7027-7035.
  5. Ye, Y.; Elabd, Y.A. Relative Chemical Stability of Alkaline Exchange Polymerized Ionic Liquids. Macromolecules 2011, 44, 8494-8503.

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