ABSTRACT
Zn-ion energy storage devices employing hydrogel electrolytes are considered as promising candidates for flexible and wearable electronics applications. This is because of their safe nature, low cost, and good mechanical characteristics. However, conventional hydrogel electrolytes face limitation at subzero temperatures. Herein, we report an antifreezing, safe, and nontoxic gel electrolyte based on the poly(vinyl alcohol) (PVA)/Zn/ethylene glycol system. The optimal gel electrolyte membrane exhibits a high ionic conductivity (15.03 mS cm-1 at room temperature) and promising antifreezing performance (9.05 mS cm-1 at -20 °C and 3.53 mS cm-1 at -40 °C). Moreover, the antifreezing gel electrolyte can suppress the growth of Zn dendrites to display a uniform Zn plating/stripping behavior. Also, a flexible antifreezing Zn-ion hybrid supercapacitor fabricated with the optimum antifreezing gel electrolyte membrane exhibits excellent electrochemical properties. The supercapacitor possesses a high specific capacity of 247.7 F g-1 at room temperature under a high working voltage of 2 V. It also displays an outstanding cyclic stability at room temperature. Moreover, the supercapacitor shows an extraordinary electrochemical behavior and cyclic stability over up to 30 000 cycles at -20 °C under a current load of 5 A g-1, demonstrating its outstanding low-temperature electrochemical performance. Besides, the antifreezing supercapacitor device also offers high flexibility under different deformation conditions. Therefore, it is believed that this work provides a simplistic method of realizing the application of flexible antifreezing Zn-ion energy storage devices in a subzero-temperature environment.
ABSTRACT
In this study, novel ionic liquid-incorporated Zn-ion conducting polymer electrolyte membranes containing polymer matrix poly (vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf), along with zinc trifluoromethanesulfonate Zn(Tf)2, are prepared and investigated. It is ascertained that the optimal membrane ILPE-Zn-4 (the mass ratio of EMITf:Zn(Tf)2:PVDF-HFP is 0.4:0.4:1), with abundant nanopores, exhibits a high amorphousness. At room temperature, the optimized electrolyte membrane offers a good value of ionic conductivity (~1.44 × 10-4 S cm-1), with a wide electrochemical stability window (~4.14 V). Moreover, the electrolyte membrane can sustain a high thermal decomposition temperature (~305 °C), and thus its mechanical performance is sufficient for practical applications. Accordingly, the ionic liquid-incorporated Zn-ion conducting polymer electrolyte could be a potential candidate for Zn-based energy storage applications.
