Researchers at Ohio State University claim to have developed more efficient and reliable potassium-oxygen batteries, which could provide a potential solution for energy storage for the national grid and longer-lasting batteries in mobile phones and laptops. In this study, the Ohio State researchers detailed their findings focusing on the construction of the battery's cathode, which stores energy from chemical reactions in metal, such as oxygen or other metals embedded in air batteries.

　　"If we want to provide a fully renewable option for the grid, we need an economical energy storage device that can store excess electricity and unleashing it in situations where people are not ready or working. Technology like this is key because it’s cheap, doesn’t use any exotic materials, and it can be produced anywhere to boost the local economy.”

　　However, in order for renewable energy to become a reliable source of energy for a regional energy grid, there needs to be a way to store excess energy collected from sunlight and wind. Companies, scientists and governments around the world are working on storage solutions, from lithium-ion batteries, the larger version of many electric vehicles, to giant, box-sized batteries made using the metal vanadium.

　　Potassium-oxygen batteries have been a potential alternative for energy storage since their invention in 2013. A team of Ohio State University researchers led by chemistry professor Yiying Wu says the battery can be more efficient than lithium-oxygen batteries while storing about twice as much energy as existing lithium-ion batteries. But potassium-oxygen batteries haven't been widely used for energy storage because, until now, they haven't had enough time to recharge to be cost-effective.

　　When the research team tried to create a potassium-oxygen battery as a viable storage solution, they ran into a roadblock. The battery degraded every time it was charged but never exceeded 5 or 10 charge cycles. This degradation occurs because oxygen gets into the anode of the battery, causing damage to the anode and making the battery itself no longer rechargeable.

　　Paul Gilmore, a doctoral student in Sundaresan's lab, began adding polymer to the cathode to see if it could protect the anode from oxygen damage. It turned out he was right, and the team realized that the expansion of the polymer played a crucial role in its performance. "The key is to find a way to bring oxygen into the battery without letting it seep into the anode," Gilmore said.

　　It is understood that the design is a bit like a human lung, with air entering the battery through the fibrous carbon layer and then encountering a second layer, which is slightly more porous, and finally ending in a third layer, which is barely porous. A third layer made of a conductive polymer allows potassium ions to pass through the cathode but restricts molecular oxygen from entering the anode. The design means the battery can be recharged at least 125 times, giving potassium-oxygen batteries 12 times longer life than previous efforts using low-cost electrolytes.

　　Sundaresan said, "This discovery shows that it is possible, but the team's tests have not yet proven that the battery can be manufactured at the scale required for grid storage. However, it does show its potential."

　　Potassium-oxygen batteries may also have potential in other applications. "Oxygen batteries have higher energy density, which means they could improve the range of electric vehicles and the battery life of portable electronics, for example," Gilmore added. "There are other challenges that must be overcome before potassium-oxygen batteries can be used in these applications." The discovery offers alternatives to lithium-ion batteries and others that rely on cobalt, a material that has been called the "blood diamond of batteries." Sourcing this material is troubling, and major companies including TESLA have announced plans to remove it from batteries entirely.

　　Sundaresan said, "It is very important that batteries for large-scale applications do not use cobalt, and it is also important that batteries can be manufactured cheaply." Lithium-oxygen batteries are one possible energy storage solution and are widely regarded as one of the most viable options. One, but it can be expensive, and many batteries rely on scarce resources including cobalt. The lithium-ion batteries used in many electric vehicles cost about US$100 per kilowatt-hour (equivalent to approximately RMB 690) based on material prices.

　　Researchers estimate that the potassium-oxygen battery costs about $44 per kilowatt-hour (equivalent to about 300 yuan).

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