Scientists Must Stop Confusing Batteries and Supercapacitors, Argue Experts

In the race for new energy storage materials, calling batteries supercapacitors wastes time and money

3 min read
Scientists Must Stop Confusing Batteries and Supercapacitors, Argue Experts
Illustration: iStockphoto

What’s in a name? More than you'd care to think about when it comes to energy storage, a team of researchers from France and the United States argued last week in the journal Science. As the energy storage field has taken off in the past five to seven years, the line between batteries and supercapacitors (also called ultracapacitors) has started to blur and scientists and engineers have become less and less consistent when naming these devices, the researchers say.

Much too often, battery materials are called supercapacitors in the scientific literature, unknowingly or perhaps deliberately, says Yury Gogotsi, a materials science and engineering professor at Drexel University and one of the authors of an essay in last week's Science. “Confusion doesn’t help progress,” he says. “Attempts to sell a poor material as a good one by using wrong terminology really holds back research and leads to a waste of money and time.”

To understand, let’s cover the basics. Batteries store charge through a redox reaction, which involves a material giving up electrons and the transport of ions through some other material. So batteries can store a lot of energy but they typically take hours to recharge.

Supercapacitors, also called ultracapacitors, store charge electrostatically on high surface-area electrodes. They store less energy but can charge or discharge in seconds. They’re commonly used to provide short bursts of power in buses and cranes and hold much promise for electric cars and the green grid.

What everyone wants is a device that can store a lot of energy and charge or discharge quickly.

Between 2006 and 2013, the number of materials research articles with the word supercapacitor or ultracapacitor in the title more than quadrupled, Gogotsi says. Technology and terminology mixups tend to happen in such rapidly growing fields. The field of graphene faces similar naming confusions.

In the case of energy storage, one reason for the confusion is that new materials—especially those on the nanoscale—combine the characteristics of the batteries and supercapacitors. This throws off scientists who are new to the field. “There are many people from a chemistry, materials science, nanoscience background who don’t know engineering rules [or] understand electrical engineering or electrochemistry well enough.”

But sometimes, scientists will deliberately try to sell a battery material as a supercapacitor, Gogotsi points out. “Numerous papers in the past year take materials like cobalt or nickel-based compounds which are typically battery materials, and represent them as pseudocapacitors,” he says. “They show up to 10 times higher capacitance than common supercapacitor materials. The problem is they are not, because they don’t have other characteristics of supercapacitors, such as thousands to a million of cycles lifetime. It’s really a battery material simply packaged and sold in literature as a supercapacitor. So an investor may invest money not understanding that they’re simply funding a type of battery development.”

So how do you define a battery versus a supercapacitor?

“The defining character is really the electrical response,” Gogotsi says. A linear change of the electric potential during discharge typically results in a constant current for a supercapacitor, whereas in a battery the current peaks at two specific potentials because of the oxidation (electron loss) and reduction (electron gain) reactions that happen at the electrodes.

Researchers need to look at the material’s electrochemical characteristics and then accurately name the device. This responsibility falls on scientists but also on journal editors and reviewers.

It’s really a matter for the entire research community, Gogotsi says. The community needs to agree on definitions and terminology, he adds. Standards would help, but they’re neither easy to create or enforce. “We know from experience that engineers like and use standards,” he says. “Scientists? Not so much.”


Image: iStockphoto

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Smokey the AI

Smart image analysis algorithms, fed by cameras carried by drones and ground vehicles, can help power companies prevent forest fires

7 min read
Smokey the AI

The 2021 Dixie Fire in northern California is suspected of being caused by Pacific Gas & Electric's equipment. The fire is the second-largest in California history.

Robyn Beck/AFP/Getty Images

The 2020 fire season in the United States was the worst in at least 70 years, with some 4 million hectares burned on the west coast alone. These West Coast fires killed at least 37 people, destroyed hundreds of structures, caused nearly US $20 billion in damage, and filled the air with smoke that threatened the health of millions of people. And this was on top of a 2018 fire season that burned more than 700,000 hectares of land in California, and a 2019-to-2020 wildfire season in Australia that torched nearly 18 million hectares.

While some of these fires started from human carelessness—or arson—far too many were sparked and spread by the electrical power infrastructure and power lines. The California Department of Forestry and Fire Protection (Cal Fire) calculates that nearly 100,000 burned hectares of those 2018 California fires were the fault of the electric power infrastructure, including the devastating Camp Fire, which wiped out most of the town of Paradise. And in July of this year, Pacific Gas & Electric indicated that blown fuses on one of its utility poles may have sparked the Dixie Fire, which burned nearly 400,000 hectares.

Until these recent disasters, most people, even those living in vulnerable areas, didn't give much thought to the fire risk from the electrical infrastructure. Power companies trim trees and inspect lines on a regular—if not particularly frequent—basis.

However, the frequency of these inspections has changed little over the years, even though climate change is causing drier and hotter weather conditions that lead up to more intense wildfires. In addition, many key electrical components are beyond their shelf lives, including insulators, transformers, arrestors, and splices that are more than 40 years old. Many transmission towers, most built for a 40-year lifespan, are entering their final decade.

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