Most supercapacitors are rigid, and the compressible supercapacitors developed so far have run into challenges. They have been made with carbon-coated polymer sponges, but the coating material tends to bunch up and compromise performance. Guruswamy Kumaraswamy, Kothandam Krishnamoorthy and colleagues at the Polymer Science and Engineering Division of the Indian National Chemical Laboratory in Pune took a different approach. The resulting supercapactior could be used for powering wearable electronic devices.
The researchers prepared polymer gels in green tea extract, which infuses the gel with polyphenols. The polyphenols converted a silver nitrate solution into a uniform coating of silver nanoparticles. Thin layers of conducting gold and poly(3,4-ethylenedioxythiophene) were then applied. And the resulting supercapacitor demonstrated power and energy densities of 2.715 kW/kg and 22 Wh/kg. This is enough to operate a heart rate monitor, LEDs or a Bluetooth module, say the researchers. They also tested the device's durability and found that it performed well even after being compressed more than 100 times.