Novel properties of graphene and other 2D materials with potential applications in energy devices and related areas

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].