All‐Organic Battery Based on Deep Eutectic Solvent and Redox‐Active Polymers

Sustainable battery concepts are of great importance for the energy storage demands of the future. Organic batteries based on redox‐active polymers are one class of promising storage systems to meet these demands, in particular when combined with environmentally friendly and safe electrolytes. Deep Eutectic Solvents (DESs) represent a class of electrolytes that can be produced from sustainable sources and exhibit in most cases no or only a small environmental impact. Because of their non‐flammability, DESs are safe, while providing an electrochemical stability window almost comparable to established battery electrolytes and much broader than typical aqueous electrolytes. Here, we report the first all‐organic battery cell based on a DES electrolyte, which in this case is composed of sodium bis (trifluoromethanesulfonyl)imide (NaTFSI) and N ‐methylacetamide (NMA) alongside the electrode active materials poly(2,2,6,6‐tetramethylpiperidin‐1‐yl‐oxyl methacrylate) (PTMA) and crosslinked poly(vinylbenzylviologen) (X‐PVBV 2+ ). The resulting cell shows two voltage plateaus at 1.07 V and 1.58 V and achieves Coulombic efficiencies of 98 %. Surprisingly, the X‐PVBV/X‐PVBV + redox couple turned out to be much more stable in NaTFSI : NMA 1 : 6 than the X‐PVBV + /X‐PVBV 2+ couple, leading to asymmetric capacity fading during cycling tests.