Polymer blend electrolytes are reemerging as an exciting class of industrially relevant electrolytes. They replace both the solvent and the salt of conventional electrolytes with polymers: termed polysolvents and polyelectrolytes, respectively. In the case of lithium batteries, the polyelectrolytes are polyanions that release lithium ions upon dissociation by polysolvents. This review defines classes of electrolytes, provides benchmarks and metrics for comparison, gives a background on polymer blends, and provides a detailed review of reports on blend-based electrolytes over the past 17 years. In particular, polyether-based polysolvents blended with single-ion conducting polyanions are covered, as well as biobased polysolvent blends mixed with lithium salts. A few outstanding reports meet polymer-based benchmarks but remain an order of magnitude below liquid electrolytes for lithium batteries. Therefore, an outlook is provided on possibilities for a major breakthrough, as are recommendations for further investigation, such as the determination of mechanical properties. Currently, polymer blend electrolytes hold great potential for high energy density but low power batteries.

A novel precision single-ion conductor with phenylsulfonyl(trifluoromethylsulfonyl)imide lithium salt covalently bound to every fifth carbon of a polyethylene backbone, p5PhTFSI-Li, was synthesized via ring opening metathesis polymerization (ROMP) followed by...

Increasing the energy density of lithium-ion batteries requires, among other advances, electrolytes that are compatible with lithium metal and next-generation cathodes. 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 polymer blend electrolytes. State of the art in these electrolytes will be reviewed including recent advancements from our team using precision polyanions with polyether solvating polymer. This presentation will cover miscibility, conductivity, and transference numbers as a function of composition and temperature. Distinct differences between blends containing the different anionic forms will be explained in the context of ion correlation. Important future directions for the subfield of polymer blend electrolytes will also be discussed.

A novel precision single ion conductor with an N-((trifluoromethyl)sulfonyl)phenylsulfonimide lithium salt covalently bound to every fifth carbon of a polyethylene backbone, p5PhTFSI-Li, was synthesized via post polymerization modification. The conversion to a trifluoromethanesulfonimide (TFSI) anion from the parent polymer bearing a phenylsulfonate anion was highly efficient (~90%) as determined by 19F-NMR analysis and corroborated through other spectroscopic methods. The bulky and flexible TFSI anion led to a reduced and observable glass transition temperature of ~199 °C and an improved thermal stability up to ~375 °C. Blending of p5PhTFSI-Li with poly(ethylene oxide) at various compositions was performed to investigate electrochemical performance and transference numbers with respect to the lithium electrode using a combination of impedance and polarization methods. At 90 °C, this system displayed high conductivity up to 2.00 X 10-4 S cm-1 and transference numbers were near unity independent of temperature, making this system highly competitive with other polyanion/polyether blend electrolytes. Investigations into the complex miscibility and phase behavior of these blends at various compositions was also probed by a combination of microscopy and differential scanning calorimetry.