Green tea supercap

Most wearable Health Tech devices depend on electricity to power their digital electronics for sensors, data storage, processing, and transmission. And in almost all cases, this means a battery. The problem is that most batteries are hard and rigid, which wearables need to be flexible and softer. Another problem with batteries: they can take a long time to recharge. But a solution may be on the horizon, based on green tea.

Many people may view green tea as a way to recharge after a busy day, but a group of scientists in India have found another use for the popular plant besides beverages. They extracted polyphenals from green tea, and used them to create a new type of supercapacitor. Supercapacitors (or “supercaps”) have the ability to store large amounts of electricity in a given space, can absorb or discharge the electricity much faster than standard batteries, and have a much longer life cycle.

Supercaps have been fabricated using plastic sponges, but when coated with carbon as a conductor, the coating “bunches up” and degrades the performance. The scientists used the green tea polyphenols to convert a solution containing silver nitrate, creating silver nanoparticles that coated the surface of the plastic sponge. They then applied thin layers of gold. The test device stored 2,715 watts per kilogram, which is significantly more than the 200 to 300 watts per kilogram for lithium-ion batteries. The researchers compressed the device more than 100 times, and it still performed well. This means that a flexible wristband could contain the power storage necessary to run a device, while providing a lighter weight and longer time between charges that we currently get with standard battery technology.