A new-and improved battery from Ohio State University may lead to all-renewable energy storage on the nation’s power grid, as well as longer-lasting batteries in cell phones and laptops.
The potassium-oxygen battery, according to researchers, could someday be used to store surplus energy gathered from the Sun and wind.
“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,” said Vishnu-Baba Sundaresan, co-author of the study published this month in the journal Batteries and Supercaps.
“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.”
The researchers estimated that their better potassium-oxygen battery will cost about $44 per kilowatt hour. By comparison, the lithium-ion batteries that power many electric cars cost around $100 per kilowatt hour at the materials level.
Potassium-oxygen batteries have been an enticing energy-storage alternative since their invention. In 2013, a team of researchers from Ohio State, led by chemistry professor Yiying Wu, showed that the batteries could be more efficient than lithium-oxygen batteries while simultaneously storing about twice the energy as existing lithium-ion batteries.
Potassium-oxygen batteries, however, have not been widely used for energy storage because they degrade. The oxygen damages the anode, limiting the battery to about five to ten charging cycles.
Paul Gilmore, a doctoral candidate in Sundaresan’s lab, discovered a way to build a set of protections and keep oxygen from seeping into the electrode.
The new design allows air to enter the battery through a fibrous carbon layer. The air then meets a second, slightly less porous layer, and finally ends at a third one, which is barely porous at all.
The third layer, made of a conducting polymer, allows potassium ions to travel throughout the cathode, while restricting molecular oxygen from reaching the anode. With the porous design, the battery can be charged at least 125 times.
The team has not yet demonstrated that the batteries can be made on the scale necessary for power-grid storage, but Prof. Sundaresan believes that the power potential is there.
“If you have a smallish battery that is cheap, then you can talk about scaling it up,” said Sundaresan. “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.”
In written responses below, Prof. Sundaresan shared with Tech Briefs the promise of potassium-oxygen batteries.
Tech Briefs: Why have potassium-oxygen batteries not caught on?
Dr. Vishnu-Baba Sundaresan: Since their invention in 2013, potassium-oxygen batteries have shown promise because of their high energy density and simple battery chemistry. They have not caught on because of two reasons:
- (i) Oxygen in its molecular form dissolves into the electrolyte at the cathode and gets to the anode. This forms potassium superoxide, or KO2, on the anode and prevents the release of K+ ions from the anode.
- (ii) The electrolyte (DME) is somewhat reactive with KO2 and leads to a lot of side products.
While (ii) is unavoidable without using a different electrolyte, our design focuses on problem (i).
Tech Briefs: How did your design improve upon current potassium oxygen batteries?
Dr. Sundaresan: Our design has a cathode with porosity that varies across its thickness. Imagine the cathode to have large pores on one side that gradually vary, forming really tiny pores that are small enough to allow K+ ions through, while blocking O2 transport. This happens via two mechanisms: the pore size obviously is one of the factors, but not the most significant.
The electrochemical properties of the conducting polymer forming the small pores in the cathode also enhance the formation of O2- (negatively charged ions). This reduction happens as the electron comes into the cathode during discharge.
This converts most of O2 into O2 - and prevents the mixing of O2 into the electrolyte. Thus, we regulate the entry of O2 into the battery at the source and hence have shown that the battery lasts longer.
Tech Briefs: What makes your battery an "economical energy storage device?”
Dr. Sundaresan: The materials used in our KO2 battery require just the necessary components and a conducting polymer that is relatively inexpensive. The innovation in our battery is in its design, and we have developed a scalable and technically relevant combination of materials required to impart necessary functional properties.
The cathode redesign uses materials that are relatively inexpensive to purchase and make in a battery. Hence, it is cheap.
Tech Briefs: How do you envision this battery impacting the power grid?
Dr. Sundaresan: Due to its low cost, and sufficiently long cycle life, such batteries will first find its application in stationary applications. Hence, I anticipate that grid management could benefit from this battery.
Tech Briefs: What are the most exciting applications that you envision?
Dr. Sundaresan: I personally believe this will be important for various applications that require high energy density. There is not much of a difference between theoretical energy density and what is achievable with KO2 battery. If you look at a study done by Prof. Juan Alonso at Stanford in 2016, this battery may meet the energy density requirements for electric propulsion in airplanes. There is a lot to be done between now and first flight with these batteries. But working towards this goal will significantly cut down emissions.
What do you think about the possibilities of Potassium-Oxygen batteries? Share your questions and comments below.