Device: Supercapacitors, the (near-ish) future of batteries
It happens to all of us: it’s the middle of the afternoon and you’re checking your smartphone for your latest messages and emails, but that red icon at the top of your phone’s display appears, warning you that your battery life is low. More than likely, your phone will die before making it through the rest of the day. And batteries can cause even more problems beyond such daily inconveniences. If an old battery is not properly disposed of (and when is the last time any of us did that?), the byproducts of batteries can leech into soil and water and can become toxic to humans, plants and animals.
But what if you didn’t have to worry about any that? What if your smartphone or other electronic devices could be charged in just a few seconds and only required charging once a week or even once a month? And what if those devices used a power supply that’s biodegradable and safe for the environment?
So how can a supercapacitor help you charge your smartphone or tablet? For starters, a supercapacitor could act as a power supply that not only charges your devices faster, but also gives those devices a charge that lasts for a longer period of time. Imagine charging your laptop in seconds and then having that charge last for up to a month. Picture a city full of electric cars that never require fuel. Think about a sky full of energy-efficient airplanes.
Supercapacitors are also more environmentally friendly than their battery counterparts. Not only are the lifespans of supercapacitors longer than batteries (as they can be charged and recharged indefinitely), but they’re also much cleaner and safer. They don’t waste much energy, making them more efficient than batteries. And supercapacitors are not made using corrosive or toxic chemicals or metals.
WHAT IS A SUPERCAPACITOR AND HOW DOES IT WORK?
A battery is comprised of electrochemical cells. These cells consist of two electrodes separated by some distance, the space between them being filled with an electrolyte, which is a compound that converts to ions when dissolved in certain solvents, like battery acid. One of these electrodes allows electrons to flow out of it while the other receives them. The energy is stored in the compounds that make up the electrodes.
Photo Credit: Wiki Commons
Supercapacitors have two conductive materials (usually metal plates) that are coated with activated carbon and are immersed in an electrolyte. One of these plates has positive ions, while the other contains negative ions. While charging, these ions accumulate on the surface of each carbon-coated plate.
In order to store energy, each carbon electrode ends up having two layers of charge coating its surface. So, for all intents and purposes, a supercapacitor is like having two capacitors for the price of one. This is why supercapacitors are sometimes referred to as ultracapacitors, as well as electric double-layer capacitors.
A capacitor generally differs from a battery in that it can store a higher amount of energy, but for a shorter period of time. This allows a supercapacitor to be used in applications that require larger amount of energy in repeated bursts (for example, a camera flash). Batteries, however, supply the bulk of energy in most devices since they can store and deliver energy over a slower period of time.
Diagram showing energy density vs. power density for batteries, capacitors and supercapacitors. Photo Credit: Wiki Commons
Why aren’t we using supercapacitors instead of batteries in our devices yet? Well, there are some inherent limitations to this technology.
OVERCOMING THE LIMITATIONS OF SUPERCAPACITORS
Like a battery, a standard capacitor stores electrical energy. Whereas a battery can both produce and store electrons, a capacitor can only store them. And although a battery can dump its charge slowly through the course of hours, a capacitor dumps its charge in mere seconds.
A Maxwell Technologies supercapacitor cell and two different multi-cell modules. Photo Credit: Wiki Commons
Supercapacitors also have a low energy density and can only hold 1/5th to 1/10th the energy of a standard battery. Because of the organic electrolyte used in supercapacitors, the fast energy discharge of a supercapacitor is much higher than that of a battery. Supercapacitors are low voltage devices: in order to achieve a practical working voltage, several need to be strung together. And at present, mass production of supercapacitors has not been something that is cost effective. For example, if you wanted to use a supercapacitor to charge your laptop now, you might have to spend hundreds of dollars on dozens of supercapacitors. When connected together, these series of supercapacitors would create a laptop that would no longer be very mobile.
Because of these limitations, using supercapacitors in our home electronics and mobile devices is not yet feasible. However, thanks to strides in scientific research, we are very close to making breakthroughs that could change this.
UCLA researchers develop new technique to scale up production of graphene micro-supercapacitors. Photo Credit: UCLA
Recently, a team of researchers at UCLA, led by Richard Kaner, uncovered a way to create graphene-based supercapacitors that charge and discharge three times faster than current lithium batteries. Graphene is the most conductive material known to man, but it can be tricky to produce and work with. The best part of this new discovery is that these graphene supercapacitors were created with a simple inexpensive DVD writer. The researchers learned that after putting a graphic oxide film on a blank DVD and then using the DVD’s laser to burn the CD, the graphic oxide is then turned into graphene. Once they had a few slices of graphene, an electrolyte was placed between the slices and a new kind of supercapacitor was born.
The researchers didn’t stop there, though. They began to play around with electrodes. Kaner said, "we placed them side by side using an interdigitated pattern, akin to interwoven fingers. This helped to maximize the accessible surface area available for each of the two electrodes while also reducing the path over which ions in the electrolyte would need to diffuse. As a result, the new supercapacitors have more charge capacity and rate capability than their stacked counterparts."
Berkeley Lab chemist John Chmiola is developing a new breed of micro-supercapacitors that could substantially boost the performance and longevity of portable electric energy storage devices. Photo Credit: Roy Kaltschmidt, Berkeley Lab Public Affairs
A few years ago, a group of researchers at the Lawrence Berkeley National Laboratory began working on creating micro-supercapacitors. Using microfabrication methods similar to those which are already being used to create microchips for electronic devices, these researchers etched electrodes of monolithic carbon film into a substrate of conductive titanium carbide. The result was micro-supercapacitors that had an energy storage density at least twice as much as existing supercapacitors.
WHEN WILL OUR ELECTRONICS HAVE SUPERCAPACITORS?
Obviously, these scientific breakthroughs still need to be tested in the real world, and that is exactly what is beginning to happen. In fact, some supercapacitors have already been put to use in a variety of ways. "Carbon-based supercaps are now used in electric buses, backup power for trucks and in cell phones to operate the flash in cameras among many other applications," Kaner said. He also said that his laboratory at UCLA is currently looking for industry partners that can assist his team in making their graphene supercapacitors on an industrial scale.
But will supercapacitors ever replace batteries? Unfortunately, Kaner doesn’t see that happening anytime soon. "Consumer devices are always trying to cram more and more energy into a small space," he stated. Obviously, this means that supercapacitors will need to be made much smaller and retain charges for longer periods of time.
At Berkeley Lab, though, researchers are working on developing new electrolytes to increase the energy storage of their micro-supercapacitors while investigating how to preserve both the million-plus charge and discharge cycles and recharge times of less than five minutes for devices. John Chmiola, a chemist with the lab, told us, "my ultimate goals are to increase energy stored to levels closer to batteries. I think this is what the end users of portable energy storage devices really desire."
It’s obviously much more likely that supercapacitors will work in our devices in tandem with existing battery technology. "The prospect of integrating batteries and supercapacitors with the micro-electromechanical systems they power represents a conceptual leap forward over existing methods for powering such devices," Chmiola said.
Thanks to the research at both UCLA and Berkeley, supercapacitors will be made smaller and cheaper, and may one day lead to more widespread use in smaller electronic devices. Let’s hope that it’s only a matter of time before the world becomes a happier, more well-charged place.