Polymer Blend Electrolytes for Batteries and Beyond

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.