Ionic Liquid-Softened Polymer Electrolyte for Anti-Drying Flexible Zinc Ion Batteries

Using solid polymer electrolytes has been proven to be an efficient strategy to address the metal dendrites and pursuing high-voltage performance. Polyethylene oxide (PEO), as a popular polymer matrix, hardly works for zinc ion batteries due to its poor zinc ionic conductivity and the poor interfacial adhesion. Here, an ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([Emim]OTF), was applied as a plasticizer to tune the room-temperature ionic conductivity and mechanical properties of PEO membrane electrolyte. Additional nanofillers ZnO were utilized to enhance the plasticity and modulus. With an optimized composition, the membrane exhibits a high modulus and soft mechanics, which can facilitate the reversible stripping/plating of Zn without formation of Zn dendrites. The optimized polymer electrolyte achieved an ionic conductivity of 2.3 × 10^–3 S cm^–1 at room temperature with a softness of 5.1 mm. By applying the resulted soft membrane electrolyte for a Zn-MnO₂ battery, a capacity of 137 mAh g^–1 is achieved at 30 mA g^–1 even without the contribution from H⁺. Such an electrolyte also works for Prussian blue analogue cathodes. Importantly, the addition of [Emim]OTF can enhance the soft contact with the electrodes, and a stable output is delivered under severe deformations for the assembled flexible devices.