Shulou(Shulou.com)05/31 Report--

From mobile phones to solar energy to electric cars, people rely more and more on batteries. With the increasing demand for safe, efficient and powerful energy storage, there is a growing demand for promising alternatives to rechargeable lithium-ion batteries. Lithium-ion batteries have been the leading technology in this field.

In a study published in the annual Proceedings of the Academy of Sciences, researchers at the Rensselaer Institute of Technology showed how they could overcome a constant challenge called dendrites to create a metal battery with almost the same performance as a lithium-ion battery but dependent on potassium, a richer and cheaper element.

The battery consists of two electrodes-- one is the cathode and the other is the anode. If you want to look at lithium-ion batteries, you will usually find a cathode made of lithium cobalt oxide and an anode made of graphite. In the process of charge and discharge, lithium ion flows back and forth between the two electrodes.

In this device, if the researchers simply use potassium cobalt oxide instead of lithium cobalt oxide, the performance will be degraded. Potassium is a larger and heavier element, so it has a lower energy density. Instead, Rensler's team hopes to improve the performance of potassium by using metal potassium instead of graphite anodes.

"in terms of performance, this is equivalent to traditional lithium-ion batteries," said Nikhil Koratkar, a professor of mechanical, aerospace and nuclear engineering at Rensselaer and lead author of the paper.

Although metal batteries show great promise, they have traditionally been plagued by metal deposits (called dendrites) on anodes. Dendrites are formed by the uneven deposition of potassium metal because the battery goes through repeated cycles of charging and discharging. Over time, Koratkar explains, the combination of potassium and metal becomes very long, almost branching.

If they grow too long, they will eventually pierce the insulating diaphragm to prevent electrodes from touching each other and short-circuit the battery. When the battery shorts, it generates heat, which may ignite the organic electrolyte in the device.

In this paper, Koratkar and his team, including Dr. Prateek Hundekar of Rensselaer and researchers at the University of Maryland, including Professor Wang Chunsheng of Chemical and Biomolecular Engineering, explain how their solution to the problem paves the way for consumers to actually use it. By operating the battery at a relatively high charge and discharge rate, they can increase the internal temperature of the battery in a well-controlled way and promote the dendrite to repair the anode by itself.

Koratkar likens the self-healing process to a pile of snow after a storm. The wind and the sun help clear the snowflakes from the snowdrifts, reduce their size, and eventually flatten them.

Similarly, although the rise in temperature in the battery does not melt potassium metal, it does help activate surface diffusion, so potassium atoms move laterally from the "stack" they create, effectively smoothing the dendrites.

"in this way, our idea is that at night or when you are not using the battery, you will have a battery management system to apply this local heat so that the dendrites can heal themselves," Koratkar said.

Karl and his team had previously shown a similar self-healing method for lithium-metal batteries, but they found that potassium-metal batteries needed less heat to complete the self-healing process. Koratkar said the promising finding means that potassium metal batteries can be more efficient, safer and practical.

"I would like to see a paradigm shift in metal batteries," Koratkar said. Metal batteries are the most effective way to make batteries; however, because of this dendrite problem, they are not feasible. With potassium, I have more hope.'

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