Towards All‐Solid‐State Polymer Batteries: Going Beyond PEO with Hybrid Concepts.

To go beyond polyethylene oxide in lithium metal batteries, a hybrid polymer/oligomer cell design is presented, where an ester oligomer provides high ionic conductivity of 0.2 mS cm−1 at 40 °C within thicker composite cathodes with active mass loadings of up to 11 mg cm−2 (LiNbO3‐coated) LiNi0.6Mn0.2Co0.2 (NMC622), while a 30 µm thin scaffold‐supported polymer electrolyte affords mechanical stability. Corresponding discharge capacities of the hybrid cells exceed 170 mAh g−1 (11 mg cm−2) or 160 mAh g−1 (6 mg cm−2) at rates of either 0.1 or 0.25 C. Multilayer pouch cells are projected to enable energy densities of 235 Wh L−1 (6 mg cm−2) and even up to 356 Wh L−1 (11 mg cm−2), clearly superior to other reported polymer‐based cell designs. Polyester electrolytes are environmentally benign and safer compared to common liquid electrolytes, while the straightforward synthesis and affordability of precursors render hybrid polyester electrolytes suitable candidates for future application in solid‐state lithium metal batteries. [ABSTRACT FROM AUTHOR]