Abstract
To effectively improve the energy density and reduce the self-discharging rate of micro-supercapacitors, an advanced strategy is required. In this study, we developed a hydroquinone (HQ)-based polymer-gel electrolyte (HQ-gel) for micro-supercapacitors. The introduced HQ redox mediators (HQ-RMs) in the gel electrolyte composites underwent additional Faradaic redox reactions and synergistically increased the overall energy density of the micro-supercapacitors. Moreover, the HQ-RMs in the gel electrolyte weakened the self-discharging behavior by providing a strong binding attachment of charged ions on the porous graphitized carbon electrodes after the redox reactions. The micro-supercapacitors with HQ gel (HQ-MSCs) showed excellent energy storage performance, including a high energy volumetric capacitance of 255 mF cm−3 at a current of 1 µA, which is 2.7 times higher than the micro-supercapacitors based on bare-gel electrolyte composites without HQ-RMs (b-MSCs). The HQ-MSCs showed comparatively low self-discharging behavior with an open circuit potential drop of 37% compared to the b-MSCs with an open circuit potential drop of 60% after 2000 s. The assembled HQ-MSCs exhibited high mechanical flexibility over the applied external tensile and compressive strains. Additionally, the HQ-MSCs show the adequate circuit compatibility within series and parallel connections and the good cycling performance of capacitance retention of 95% after 3000 cycles.
Highlights
Recent studies have demonstrated the potential of flexible micro-supercapacitors for supplying energy and electricity to future flexible and wearable electronics such as rollable displays, human-implanted devices, and high-end robotics [1,2,3]
Carbon materials can be handled on flexible substrates, and their electrical and chemical properties are well tailored by a simple post-treatment process, inducing high electrochemical energy storage performance [6,7]
The gold and nitrogen doping on the carbon electrode sample can increase the conductivity and wettability of the carbon electrode, inducing the improved electrochemical performance [8]
Summary
Recent studies have demonstrated the potential of flexible micro-supercapacitors for supplying energy and electricity to future flexible and wearable electronics such as rollable displays, human-implanted devices, and high-end robotics [1,2,3]. Carbon materials can be handled on flexible substrates, and their electrical and chemical properties are well tailored by a simple post-treatment process, inducing high electrochemical energy storage performance [6,7]. The energy density of carbon-based electrodes based on electric double layer capacitor (EDLC) lies in the range of 0.1~3 Wh kg−1 [12], but in a range of over 100 Wh kg−1 for Li ion batteries. There is another type of supercapacitor (pseudocapacitors, with an energy density of about 10 Wh kg−1 ), but they store charges through
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