Poly(Vinyl Alcohol) Hydrogel Containingdeep Eutectic Solvents as Electrolytes with Co-Nonsolvency Effect for Anti-Freezing Zinc-Ion Hybrid Supercapacitors

Abstract

A flexible and anti-freezing poly(vinyl alcohol) (PVA) hydrogel electrolyte containing Zn(ClO4)2·6H2O/ethylene glycol (EG) deep eutectic solvents (DES) and water is designed based on the effect of co-nonsolvency in the presence of sodium dodecyl benzene sulfonate (SDBS). The (SO3R)− anions in SDBS own good affinity with Zn2+. Therefore, the anions can effectively regulate the solvation sheath of hydrated Zn2+ ions, releasing more ClO4- ions and H2O in the solvation structure. The ClO4- ions, EG, and SDBS synergistically destroy the consecutive hydrogen bonding network among H2O molecules, depressing the solid-liquid transition temperature of the DES-SxP gel to -56.98 oC. Moreover, the generation of new H-bonds among ClO4- ions, EG, and SDBS with H2O immeasurably prohibits the activity of H2O, disrupting the hazardous side reactions as well as dendrites related to H2O molecules and extremely extending the electrochemical window (3.04 V). The assembled Zn||Zn symmetrical cells can cycle over 980 h at 1 mA cm-1 at room temperature. The excellent cyclic stability improves to 8000 cycles with a considerable specific capacity of 88.75 mAh g-1 at 5 A g-1 and 20000 cycles with 65.71 mAh g-1 at 10 A g-1 under -20 oC.

Keywords: Deep Eutectic Solvents, co-nonsolvency effect, freezing-tolerance capability, Hydrogel Electrolyte