Electric vehicle company Tesla garnered headlines and worldwide attention last year when it announced a $5 billion Gigafactory in Nevada to make lithium-ion (Li-ion) battery packs for electric vehicles. And Tesla isn’t alone. Dollars are flowing into battery development as companies look for power packs that can quickly charge and affordably supply hundreds of miles of vehicle range.
Those huge dollar volumes can make it hard for people to accept alternatives to batteries in electrically driven cars, says Chad Hall, co-founder and vice president of marketing for Ioxus, a company that makes ultracapacitors. A tiny slice of the alternative-energy vehicle world compared to batteries, ultracapacitors are growing in popularity thanks to falling prices and greater awareness from engineers and designers. But Hall says the battery hype can be hard to cut through.
“Everybody thought Li-ion was going to be the horse to pick. Billions of dollars went in that direction because the cost per kilowatt hour was supposed to come down dramatically. That really hasn’t happened,” Hall says. “You have tremendous lobbying behind the battery guys. You have money spent on Li-ion, and people want to recoup those investments.”
In that environment, ultracapacitor use has been able to grow by filling specific niches – buses, industrial off-highway equipment, some fuel-cell vehicles – but hasn’t found the same use in passenger cars, especially in the United States. For that to happen, Hall says his company and others have to make a vigorous case for the technology and win over engineers who have been selecting batteries because that’s a technology the auto industry has used for more than a century.
Unlike batteries, which store electricity electrochemically and release power through a chemical reaction, ultracapacitors store charges electrostatically. Much in the same way that rubbing a balloon against someone’s hair creates enough static electricity to get the balloon to stick to the person’s head, ultracapacitors store vast amounts of charge in the microscopic pores of their systems.
The lack of a chemical reaction means they can operate equally well at high or low temperatures, unlike batteries that lose effectiveness in colder weather, Hall says. The lack of a chemical reaction means they can accept large charges almost instantly and discharge that power without damaging their internal structures. Batteries tend to heat up when accepting or delivering large charges, and that heat can damage cells, lowering usable life.
“Ultracapacitors don’t care about depth of discharge or state of charge,” Hall says. “They work the same way no matter what’s going on. With batteries, you have to know those things because it determines the charge acceptance of the system.”
Those heat and charge issues are critical to vehicle designers because they determine the size and the weight of power systems in hybrid and all-electric cars. When designing hybrids and electrics, engineers specify vastly oversized batteries then use a small portion of the battery’s capacity – cycling between a 30% charge and a 70% charge typically – to avoid heat generation that would lower the system’s lifespan. Those oversized batteries add weight to the cars, reducing the range of all-electrics or lowering the fuel economy of hybrids.
The big problem with using batteries in hybrids and electrics, Hall says, is that designers are trying to get two functions out of the same device – energy storage and power delivery/absorption. Batteries are great at storing energy, but they struggle to deliver it in large quantities when needed, and they can’t absorb it in big chunks. Ultracapacitors, on the other hand, aren’t very good at storing energy long term, but they have no problem receiving or delivering power.
“I use a teacup versus teapot analogy,” Hall says. “The battery is the teapot. It holds a lot of water, but it has a small opening, so you can only get a certain amount of water in or out at once. The ultracapacitor is the teacup. If it’s full, you can dump all of that water out at once. If you dump a bucket of water on the table, you’ll fill it up instantly.”
Designers could craft a similar system for cars, he adds, using the ultracapacitor as a sort of buffer between the battery and the drive system. The ultracapacitor could receive all of the power generated by the car’s regenerative braking system while it’s driving and allow that energy to trickle into the battery for longer-term storage. Or the ultracapacitors could deliver the power needed to get a car from a standstill to 45mph, delivering lots of power quickly, and letting batteries take over at cruising speed when power demands are much lower.
“We’ve done this in forklifts, taken over the charge/discharge cycle with an ultracapacitor and replaced the power-oriented battery with a high-energy battery,” Hall says, adding that the combined systems were 20% smaller. “That battery never sees those power spikes, so it lasts four to eight times longer.”
The combined system is more expensive than using a large battery by itself, he adds, but the long-term ownership costs are lower due to increased service life.
Where Hall sees the biggest opportunity, and where Ioxus sees some success in Europe, are mild hybrids – vehicles that shut off their engines while stopped and get some assistance from electric motors at low speeds, but ones that can’t run entirely on electricity, even for short distances. Mazda is using an ultracapacitor-based mild hybrid system in the 6 sedan in North America, Europe, and Asia. Peugeot also uses Ioxus ultracapacitors.
Automakers have used mild hybrids as a less-expensive option to boost fuel economy. Because the hybrid system only activates right before or after a stop, or to provide a small boost when accelerating at highway speeds, the systems use much smaller batteries than full-hybrid (also called strong hybrid) systems do.
“You don’t have the energy storage needs with mild hybrids, so that’s a much easier argument for us to make,” Hall says.
Mild hybrids that have only the ultracapacitor, can eliminate the storage battery entirely, reducing weight and cost.
He adds that he hopes the ultracapacitor successes with a few European products will translate into more mainstream automotive work. Ioxus has test programs going on with many major automakers, so Hall believes 2017 through 2018 could see a big increase in the number of non-battery hybrids on the market.
“During the past 10 years, cost of ultracaps have gone down 99% and performance has gone up 5 times. There are more competitors, more investment dollars, and more customers in different industries. All of that lowers costs,” Hall says. “The costs will further come down with volume. If we can get into automotive production, that’s our big opportunity for high volumes.”
Harnessing electrostatic power
Ultracapacitor manufacturers create vast amounts of surface area by using microscopically porous materials.
One farad, the measure of electric capacitance to effectively store 1V, requires nearly a football field’s worth of surface area, says Chad Hall, co-founder of ultracapacitor producer Ioxus. He adds, “With ultracapacitors, we’re putting 3,000 farads in the size of a beer can.”
The main ingredient is carbon – refined charcoal, effectively – broken into particles 5nm to 8nm in diameter. Thin layers of film or paper separators divide layers of the carbon from each other.
Positive or negative charges move along the surfaces of the carbon, and positive or negative ions travel from those layers, through the separator, to positive or negative terminals. The systems can either be stacked together as square or rectangular cells or rolled into cylinders.
Halls says that unlike advanced battery chemistries that rely on rare materials, ultracapacitors use inexpensive, widely available components. The most expensive part of the process, he says, is the purification process for the carbon.
About the author: Robert Schoenberger is the editor of TMV and can be reached at 216.393.0271 or firstname.lastname@example.org.