Increasing the energy density of lithium-ion batteries requires, among other advances, electrolytes that are compatible with lithium metal and other next generation electrodes. Polymer electrolytes play an important role in this regard, but overcoming slow ion transport is a major challenge. Hybrid electrolytes that combine fast ion transport of ceramic electrolytes and processability of polymer electrolytes are promising. To take advantage of transport in both phases, transference numbers should be comparable. Thus, single-ion conducting polymer electrolytes have received major focus in recent years. In addition to the benefit in hybrid electrolytes, single-ion conduction yields numerous transport and efficiency advantages in neat polymer electrolytes. Due to formulation simplicity and motivated by block copolymer advancements, our team has focused on blends of precision polyanions with polyether solvating polymer. In particular, we have examined poly(4-phenylcyclopentene) (p5Ph) with two different anion functionalities, sulfonate (S) and N-((trifluoromethyl)sulfonyl)phenylsulfonimide (TFSI), both in lithium salt form. The parent polymer, p5Ph, was synthesized via ring opening metathesis polymerization (ROMP) and hydrogenated resulting in a polyethylene backbone with a pendant phenyl every 5 carbons.¹ Potential advantages of this polymer over polystyrene (PS) include much lower glass transition temperature (T_g ~17 °C versus ~105 °C for PS)^1-2 and facile functionalization to the sulfonated lithium salt form (p5PhS-Li)³ and to the TFSI form (p5PhTFSI-Li). Both of the polyelectrolytes have been blended with poly(ethylene oxide) (PEO). This presentation will report the results of miscibility, conductivity, and transference number studies as a function of composition and temperature. Distinct differences between blends containing the different anionic forms will be explained in the context of thermodynamic simulations⁴ and charge delocalization. Transport in the TFSI-based blend are competitive with some of the best performing polymer blend electrolyte reports. Important future directions for the subfield of polymer blend electrolytes will also be discussed.

References

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