Scientists Find a Way to Build Potassium-Oxygen Batteries that Last Longer

Scientists have developed a more reliable, more efficient, potassium-oxygen battery, a step toward a prospective solution for energy storage on the nation’s power grid and more durable batteries in laptops and cell phones.

Image credit: Ohio State University

In a research reported in May 2019 in the journal Batteries and Supercaps, scientists from the Ohio State University explained their findings focused on the development of the battery’s cathode, which stores the energy generated by a chemical reaction in a metal-oxygen or metal-air battery. According to the scientists, the finding could make renewable energy sources such as wind and solar more feasible options for the power grid through more economical and more efficient energy storage.

If you want to go to an all-renewable option for the power grid, you need economical energy storage devices that can store excess power and give that power back out when you don’t have the source ready or working. Technology like this is key because it is cheap, it doesn’t use any exotic materials, and it can be made anywhere and promote the local economy.

Vishnu-Baba Sundaresan, Study Co-Author and Professor, Mechanical and Aerospace Engineering, Ohio State

Renewable energy sources do not release carbon dioxide, hence they do not contribute to global warming; however, they produce energy only when the wind is blowing or the sun is shining. There should be a way to store excess energy harvested from wind and sunshine, only then they can be reliable sources of power for an area’s energy grid.

Researchers, governments, and companies worldwide are researching on storage solutions, ranging from lithium-ion batteries—larger versions of those in several electric vehicles—to huge batteries the size of a big-box store developed using the metal vanadium.

Since they were invented in 2013, potassium-oxygen batteries have been used as a prospective alternative for energy storage. A team of scientists from Ohio State, headed by chemistry professor Yiying Wu, demonstrated that the batteries could be more efficient when compared to lithium-oxygen batteries while simultaneously storing around twice the energy as lithium-ion batteries that are currently used. However, potassium-oxygen batteries have not been extensively used for energy storage to date as they haven’t been able to recharge adequate times to be cost-effective.

As research groups attempted to develop a potassium-oxygen battery that could be a feasible storage solution, they always got into trouble: The battery deteriorated with each charge, never lasting more than five or ten charging cycles, which is away from what is needed to make the battery a cost-effective solution for storing power. That degradation occurred due to the entering of oxygen into the battery’s anode, the component that enables electrons to charge a device, be it a power grid or a cell phone. The oxygen caused the anode to degrade such that the battery itself could not supply charge anymore.

Paul Gilmore, a doctoral candidate in Sundaresan’s lab, started integrating polymers into the cathode to check if he could protect the anode from oxygen. He thought that if he could find a method to do that, it would offer potassium-oxygen batteries a chance at longer lives. He was eventually right: The group understood that swelling in the polymer played a key role in its performance. Gilmore stated that the key was to find a way to bring oxygen into the battery—essential for it to work—without permitting oxygen to diffuse the anode.

This design works somewhat akin to human lungs: Air enters the battery via a fibrous carbon layer, subsequently reaches a second layer that is rather less porous and finally reaches a third layer, which is hardly porous at all. That third layer, composed of the conducting polymer, enables potassium ions to travel all through the cathode but blocks molecular oxygen from entering the anode. The design implies that the battery can be charged at least 125 times—offering potassium-oxygen batteries over 12 times the longevity they earlier had with low-cost electrolytes.

According to Sundaresan, the finding demonstrates that this is possible; however, the team’s tests haven’t shown that the batteries can be created on the scale needed for power-grid storage. However, it holds promise.

Gilmore stated that there may also be a possibility for potassium-oxygen batteries to be valuable in other applications.

Oxygen batteries have higher energy density, which means they can improve the range of electric vehicles and battery life of portable electronics, for example, though other challenges must be overcome before potassium-oxygen batteries are viable for these applications,” he said.

Also, the finding provides an alternative to lithium-ion batteries and others that depend on cobalt, a material that has been known as “the blood diamond of batteries.” The material is very difficult to mine that leading companies, like TESLA, have announced their strategies to remove it from batteries completely.

It is very important that batteries intended for large-scale applications do not use cobalt,” Sundaresan said.

Furthermore, it is essential for the battery to be made cheaply. Lithium-oxygen batteries—a potential energy storage solution that is extensively regarded as one of the most feasible choices—can be expensive, and many depend on sparse resources, such as cobalt. The lithium-ion batteries that power a number of electric cars cost approximately $100 per kilowatt hour at the level of the material.

The scientists calculated that this potassium-oxygen battery will cost about $44 per kilowatt hour.

When it comes to batteries, one size does not fit all. For potassium-oxygen and lithium-oxygen batteries, the cost has been prohibitive to use them as grid power backup. But now that we’ve shown that we can make a battery this cheap and this stable, then it makes it compete with other technologies for grid power backup. If you have a smallish battery that is cheap, then you can talk about scaling it up. If you have a smallish battery that is $1,000 a pop, then scaling it up is just not possible. This opens the door for scaling it up.

Vishnu-Baba Sundaresan, Study Co-Author and Professor, Mechanical and Aerospace Engineering, Ohio State

This research was funded by a grant from the National Science Foundation.

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