Ohio State beats own world record in super capacitors

For weekend warriors making routine repairs around the house, the electric drill is always a gamble. Rarely is it ever charged, and once charged, rarely does it finish a project without dying out.

A team of electrical and computer engineers (ECE) at The Ohio State University is working on the answer to this and many other power conundrums. Their results are already breaking world records.

By advancing beyond fuel cells and batteries as power sources, they are paving the way for supercapacitors. Imagine cell phones and drills keeping steady power, without slowly dying out after countless recharging over the years.

Ohio State ECE Professor Wu Lu currently holds the world record for designing the longest-lasting rechargeable power source through his work in graphene supercapacitors. In 2015, the Journal of Power Sources published his research in this area, as it relates to high-grade electrical vehicles. The article gained national attention for Ohio State in this area.

A short educational moment about the difference between fuel cells, batteries and capacitors: The advantage of fuel cells and batteries is they store more energy. While this is commendable, their power density diminishes rapidly.

“A capacitor is just the reverse,” Lu said. “Capacitors have very high power density. Within a given period of time, they can deliver more power. That’s why they can have an application in electric vehicles. Ideally, with these devices, the properties one would like to have is both high-power density and high energy density, and fast charging time, used over a long period of time.”

He also explained why batteries and fuel cells continue to fall short as long-term power solutions.

“Batteries can only be charged a very limited number of times. Everybody has such an experience,” Lu said. “Cell phones, for example, you see very significant degradation after just a few months. Typical lifetime of the battery is one to two years. Then, you either need a new battery for your phone, or a new phone. “

An advantage of the capacitor, he said, is it charges an “almost unlimited” number of times, with very little degradation. What Lu and his team already proved is throughout 10,000 recharging cycles, the degradation of a capacitor is around just 5-6 percent.

“This happens only in the first couple thousand charges. Then it becomes stabilized and doesn’t degrade anymore. That’s a great advantage,” he said. 

Lu said this is the goal of the project, “achieving high power density and high energy density, simultaneously, in a device.”

His team’s current work, “Graphene supercapacitor with both high power and energy density,” published in Nanotechnology, proves their idea is capable of even greater power than previously reported.

“Indeed, for graphene-based superconductors this is still the world record,” Lu said.

The key, he said, is creating porous graphene materials, which allow for greater power absorption under the surface.

“That’s why it can store more charge. The pore size must be optimal and uniform in nanometers,” he said.

While creating these materials is possible in the lab, they are still too expensive to create on the mass market.

ECE PhD student Hao Yang said that as the cost for producing such uniform materials decreases, so does their potential for improving renewable power sources.

“Imagine consumer electronics, cell phone and tablets, charged quickly within a few minutes. Charged many times,” he said.

This is especially important for providing ideal acceleration for electrical vehicles, as well as renewable energy storage for wind turbines, or even long-lasting power for trains, subways, city buses – even those pesky power tools.

“Within a few miles, city buses have many, many stops. The idea is when the energy is finished you want to be quickly charged. You get to the terminal; the driver has five minutes rest before the next cycle. Terminal stopping is good enough for the supercapacitor to charge,” Yang said.

He agreed the major obstacle is the cost of manufacturing. The process can produce tons of these materials.

“But the results are not so ideal for applications because the materials don’t have the uniform properties,” Yang said.

Their research proposes new ways to scale up manufacturing of the desired materials, without having to rely upon the typical higher temperatures (usually upwards of 600 Celsius needed. They can achieve this under lower temperatures, less than 200 Celsius.