Supercapacitors have become ubiquitous at this point. They provide everything from back-up power for mobile phones to extending the battery life of devices that sometimes need quick bursts of power like a digital camera’s zoom feature. These supercapacitors—sometimes referred to as electrochemical double layer capacitors (EDLCs)—come in a growing variety of shapes, size and applications, the breadth of which you can see on display in the data sheets maintained by Arrow Electronics.
However, as wide as the application of supercapacitors has become, the aim has been for them to reach a far wider set of applications that have been to-date the sole domain of batteries, in particular the application of powering all-electric vehicles (EVs). To do this, a great deal of research has been focused on improving the electrode material so the supercapacitors can hold more charge.
Supercapacitors have a much higher power density than batteries, which means that they can both deliver and absorb energy from the load much faster than batteries. In EV applications this would translate into being able to charge an EV in a matter of minutes as opposed to hours. This would be great for EVs but supercapacitors lack the energy density of batteries, which is the amount of energy they can store.
On average, most run-of-the-mill supercapacitors only have energy densities of around 8-10 Watt-hours per kilogram (Wh/kg). Even lab prototype supercapacitors made from graphene are only reaching 130Wh/kg, which is pretty far below the average Li-ion battery that has an energy density of around 200Wh/kg.
In an analysis piece, Nick Powers, an application marketing manager for Arrow Electronics, quotes Jamil Kawa, a scientist at Synopsys, on this closing gap between the energy densities of supercapacitors and batteries who explains: “Historically the ability of capacitors to act as a ‘store of energy’ was so miniscule compared to batteries that they were never seriously considered as an alternative. Supercapacitors and ultracapacitors have dramatically increased the volumetric capacity for energy storage. It is not yet on par with batteries or fuel cells, but is close enough to be competitive with them given that it has some qualities that are superior to batteries.”
Powers also notes that supercapacitors can be charged and discharged for all practical purposes nearly infinitely, whereas a battery loses its ability to be recharged after several hundred or possibly a thousand cycles. When this charge/discharge lifecycle is translated into how long an EV can run on a set of Li-ion batteries, it could be around 10 years. However, when those 10 years do come, you can be facing a pretty hefty price tag. Removing that potential price tag after 10 years of ownership seems a pretty attractive benefit of supercapacitors.
But the widening range of applications for supercapacitors is not limited to encompassing a new generation of EVs. As Nick Powers at Arrow points out, supercapacitors could be what ends up powering the Internet of Things (IoT). The devices that make up the IoT will likely depend on some kind of energy-harvesting mechanism that will make the incorporation of small but powerful energy storage devices like supercapacitors a critical element of these devices.
While the applications for supercapacitors will evolve, they will likely remain largely in their role as a companion to batteries. Nonetheless, supercapacitors look poised to start extending into those applications in which large capacitance requirements have previously excluded them.