Abstract:
Energy storage devices are prevalent in our everyday lives, from powering laptops to mobile phones and to serve as backup energy supplies in numerous electronic applications [1]. The emerging electronic markets and technologies will continue to increase the importance of lightweight, affordable and long-life energy storage devices. Batteries and capacitors are widely used devices in energy storage applications. Traditional capacitors store energy through electrostatic charging at their electrode-electrolyte interfaces under an applied potential, whereas batteries store energy through electrochemical reactions that typically occur throughout the entire bulk of the electrode active material [2]. This is the reason why batteries store more energy than capacitors. The power/energy densities of the devices are captured in the Ragone plot shown Figure 1. Energy density is a measure of energy stored in a given size or mass. A device with higher energy density can power a load longer than a low energy density device for the same physical size or mass and its unit is Wh/kg. Power density measures how quickly the device can deliver energy. In other words, it is equivalent to the maximum current one can draw from a device of a given size and its unit is W/kg [2].
Although capacitors are not viable for large-scale or high-energy storage, they have found commercial use in applications that need fast, pulsed power (car acceleration, tramways, cranes, forklifts, emergency systeM.S. etc.,) and levelling of current fluctuations in control electronics [3]. Capacitors have certain advantages over batteries in low-energy applications because they are cost-effective, can be charged significantly faster and have longer lifetimes. The latter two features are result of the absence of electrochemical reactions in appropriately designed capacitors [2].
