Toughened redox-active hydrogel as flexible electrolyte and separator applying supercapacitors with superior performance

Abstract

Gel electrolytes with a reasonable ionic conductivity and high mechanical strength have drawn great interest for applications in flexible and wearable devices. However, the demand for gel electrolytes that combine high mechanical strength and excellent electrochemical performances remains a challenge. Here, a novel redox-active gel electrolyte was prepared by adding AQQS (1-anthraquinone sulfonic acid sodium) to a PVA (polyvinyl alcohol)–H₂SO₄ system using a simple solution-mixing/casting method, which possesses not only excellent mechanical strength but also a high ionic conductivity of 28.5 mS cm⁻¹. Surprisingly, the as-fabricated supercapacitor can be operated at a wide voltage range of 0–1.4 V, which is much larger than that of the previously reported active electrolyte based supercapacitors (about 1.0 V). Furthermore, the supercapacitor exhibits superior electrochemical performance such as a maximum specific capacitance of 448 F g⁻¹ at a current density of 0.5 A g⁻¹, a high specific energy of 30.5 W h kg⁻¹ at a specific power of 350 W kg⁻¹ and good cycling stability with 91% specific capacitance retention after 1000 cycles. Additionally, such a device displays remarkably stable capacitive performance with the gel electrolyte even under a large tensile strain of 100%, a high pressure of 2000 kPa or fold states. The results doubtlessly demonstrate that the toughened redox-active gel polymer is a promising electrolyte candidate for developing high energy density flexible energy storage devices.