374514 Polymerized Ionic Liquid Block Copolymers As Solid-State Polymer Electrolytes for Lithium-Ion Batteries

Monday, November 17, 2014
Galleria Exhibit Hall (Hilton Atlanta)
Jacob Nykaza and Yossef A. Elabd, Department of Chemical and Biological Engineering, Drexel University, Philadelphia, PA

Replacing liquid-based electrolytes with solid-state polymer electrolytes (SPEs) can alleviate safety and stability concerns, while offering other attractive properties, such as thin-film forming ability, flexibility, and transparency. Ideal SPEs expertly engineering within a solid-state battery will require high lithium ion conductivities and high mechanical strength to result in high overall storage capacity/energy density and high stability and cyclability in a lithium-ion battery. Block copolymers are a well-explored material platform for this application because it combines the properties of high ionic conductivity and high strength in a nanostructured solid-state film due to covalent connection of two dissimilar polymer chains in sequential chain architecture. Herein, we present new block copolymer chemistry, where the conductive block is a polymerized ion liquid (PIL), i.e., PIL block copolymer. PILs possess unique physiochemical properties, such as high solid-state ionic conductivity, high chemical, thermal, and electrochemical stability, and widely tunable physical properties. PIL block copolymers are a new type of SPE that combine the advantages of block copolymers (nanostructured morphology) and PILs (unique physiochemical properties). In this work, the PIL diblock copolymer poly(MMA-b-MUBIm-TFSI) with an ionic PIL component (1-[(2-methacryloyloxy)undecyl]-3-butylimidazolium bis(trifluoromethane)sulfonimide) (MUBIm-TFSI) and a non-ionic component (MMA) was synthesized via reverse addition fragmentation chain transfer (RAFT) polymerization technique followed by post-functionalization and ion exchange. SPEs consisting of this PIL block copolymer and lithium salt/IL were fabricated via solution casting at various lithium salt/IL compositions ranging from 0 to 0.5 mol ratio of (salt/IL)/polymer. Interestingly, the PIL diblock copolymer exhibited no microphase separation over the entire salt/IL composition range explored evidenced by no scattering peak in small-angle X-ray scattering (SAXS) and only one broad glass transition temperature (Tg) in differential scanning calorimetry (DSC). The Tg decreased from 39 to 10 °C with increasing salt/IL composition. The temperature-dependent ionic conductivity increased by three orders of magnitude with increasing salt/IL composition, with a half an order of magnitude increase from 0.3 to 0.4 mol ratio and over one and a half orders of magnitude increase from 0.4 to 0.5 mol ratio, which was surprising for this small Tg depression between each ratio. These results suggest that ionic conductivity can be significantly improved without microphase separation and that salt-polymer compatibility may play a significant role on conductivity.

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