“While batteries must be charged at a constant voltage, a supercapacitor charges most efficiently by drawing the maximum current that the source can supply, irrespective of voltage,” said Professor Husam Alshareef.
The team has developed integrated microsupercapacitors with vertically-scaled three-dimensional porous current collectors made from nickel foams which increase the surface area.
“This three-dimensional porous architecture allows excellent electrolyte permeability, good conductivity and faster ion transportation with maximum mass-loading of active material, which increase energy and power density in a given area,” Prof Alshareef added.
The microsupercapacitors were also asymmetric, using two different electrode materials for the cathode (nickel cobalt sulphide) and anode (carbon nanofibre), which nearly doubled the operating voltage. As a result, while delivering high power density (4mW/cm2), the microsupercapacitors had an energy density of 200µWh/cm2.
This is said to be superior to other microsupercapacitors, which achieve between one and 40µWh/cm2. These capacities were maintained even after 10,000 operating cycles.
According to the researchers, supercapacitors could function for self-powered system applications where the power source may be intermittent.
