Supercapacitors, also known as ultracapacitors or electric double-layer capacitors, are crucial components in modern electrical systems. They are commonly used in regenerative braking systems for vehicles, power supplies, and various electronic devices. These energy storage devices, unlike batteries that store energy through chemical reactions, use ion separation to store energy.

While traditional capacitors are widely used for their ability to rapidly release energy, supercapacitors offer an advanced solution with much higher energy storage capacity. They achieve this by using high-surface-area electrodes and a liquid electrolyte that contains ions. In essence, supercapacitors are designed to store and discharge electrical energy more efficiently than conventional capacitors.

Aqueous supercapacitors, which rely on a water-based electrolyte, offer safety and environmental benefits. However, they face significant practical challenges that hinder their performance. Despite their potential, these supercapacitors struggle to achieve high energy storage capacity and stability under various conditions.

Supercapacitors are capable of charging and discharging in mere seconds, much faster than standard batteries. However, this rapid charging ability comes with a limitation: while they excel at releasing energy instantly, they are not designed for long-term power storage. The structure of supercapacitors consists of two electrodes, an electrolyte (usually ionized water), and a separator. When an external voltage is applied, ions in the electrolyte move toward the electrodes, forming double charge layers. As voltage increases, more charge is stored.

But the challenge arises when water breaks down into ions at low voltages. This reaction limits the energy storage capacity of aqueous supercapacitors. Moreover, water’s tendency to freeze or evaporate at extreme temperatures further complicates their use, preventing the device from performing optimally.

These limitations have prompted researchers to explore alternatives to improve the performance and practical viability of aqueous supercapacitors.

In response to these challenges, a team of researchers from China has developed an innovative hybrid electrolyte design to overcome the limitations of conventional aqueous supercapacitors. This breakthrough involves a ternary (three-component) electrolyte that combines water, an ionic liquid called EMIMNTf₂, and a potassium salt known as potassium trifluoromethanesulfonate (KOTf).

Normally, the ionic liquid doesn’t mix well with water. However, the addition of KOTf facilitates the mixing process. Through a series of solubility tests, the researchers discovered that the combination of these components changes the arrangement of water molecules around the potassium ions. This alteration prevents unwanted breakdown reactions that typically occur at higher voltages. By reducing the number of free water molecules, the new electrolyte composition enhances the supercapacitor’s ability to withstand higher voltages while minimizing harmful reactions.

In addition to improving voltage tolerance, this new hybrid electrolyte also provides thermal stability. Unlike pure water-based electrolytes, which lose functionality at extreme temperatures, the hybrid electrolyte remains stable in both low and high-temperature environments.

The newly designed hybrid electrolyte demonstrated impressive performance in tests, allowing the supercapacitor to function at voltages as high as 3.37 volts. This represents nearly three times the voltage tolerance of traditional aqueous supercapacitors. Furthermore, the device exhibited remarkable temperature stability, operating reliably from 32°F to 212°F (0 to 100°C). At elevated temperatures around 140°F (60°C), the supercapacitor retained 81.8% of its capacity after 10,000 charge cycles, showcasing its durability and long-term energy storage capabilities.

This groundbreaking hybrid electrolyte design not only improves voltage tolerance but also enhances thermal stability, opening the door for more efficient and reliable supercapacitors in a wide range of applications. With this advancement, supercapacitors may soon overcome the limitations of aqueous designs and contribute to more sustainable and high-performance energy storage systems in the future.

By Impact Lab