Supercapacitors are considered the most advanced, promising, and emerging energy-storing devices. They are portrayed as modern state-of-the-art electrochemical devices and are highly explored for a large number of emerging energy-storing technologies.
(Photo: Wikimedia Commons/ Windell Oskay)
Challenges in Creating Supercapacitors
Supercapacitors are excellent at capturing and storing energy. Various materials and fabrication methods can make them thin, flexible, and appropriate for use in wearable or implantable electronics, such as smartwatches or pacemakers. However, these approaches tend to be intricate and costly.
Two-dimensional materials are also widely used in supercapacitors due to their enormous surface area, stability, and ease of charge exchange. Recently, flexible 2D supercapacitors have been highly attractive for many emerging portable, lightweight consumer devices.
However, flexible 2D supercapacitors usually suffer from complicated and time-consuming fabrication processes and poor mechanical endurance. Since they are typical 2D flat structures, the interface between the electrolyte and the electrodes can be displaced under repeated mechanical deformation. This makes the interfacial contact less effective.
The mismatched bulk strain between the electrolyte layers and the electrode usually causes the inevitable interfacial displacement and delamination during repeated mechanical deformation. It gives rise to a crucial increase in the interfacial contact resistance between electrolyte layers and electrodes.
The resulting charge/discharge rate is severely diminished, while the energy storage performance and stability are suppressed. Additionally, the integrated, flexible supercapacitor devices in series for high-voltage output still rely on many conducting metal wires. This essentially limits their deformable tolerance, flexibility, and miniaturization for practical applications.
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Addressing Issues of Flexible 2D Supercapacitors
At Jilin University in China, a team of researchers has developed a type of all-in-one adhesive electrode that solves one of the major issues concerning advancing flexible 2D supercapacitors. The details of their study are discussed in the paper "Taming of heteropoly acids into adhesive electrodes using amino acids for the development of flexible two-dimensional supercapacitors."
Led by Wen Li, the team created an adhesive electrode that simplifies the fabrication process and overcomes the interfacial displacement of conventional supercapacitors. This type of electrode helps make the components work synergistically.
Li and his colleagues combined heteropoly acids (HPA) with amino acids and carbon materials to solve interfacial problems and eliminate wires. This enabled the researchers to construct a type of wet adhesive that simultaneously carries redox properties, adhesiveness, electron conduction, and mechanical deformation. HPAs serve as a class of inorganic nano-sized clusters with reversible and fast redox activity. They allow the supercapacitor to charge and discharge energy quickly and reliably.
The amino acids help the HPAs become more flexible, while the carbon materials contribute to electronic conduction. Injecting a gel-electrolyte connects the gap between the parallel electrodes, enabling the creation of a flexible 2D capacitor.
The experts found that the carbon components enhance electronic conduction, while the chemistry of the amino acids contributes to the interfacial adhesion. Meanwhile, the HPA clusters prevent larger structures from forming and provide the electrode with electron transfer and storage ability.
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