Sunday, September 25, 2022

Extreme cold can crack lithium-ion battery materials, reducing performance

It’s not exactly a mystery that batteries don’t go very well with extreme temperatures, whether hot or cold. Understanding the behavior of lithium-ion batteries under extreme conditions is key to the broad adoption of these batteries in various applications scenarios. Poor cold-weather performance of the lithium-ion batteries has consequences for some of their most important applications – everything from starting an electric car in a Wisconsin winter to flying a drone on Mars.

While this issue is frequently mentioned and has received much attention from researchers and manufacturers, the exact mechanisms leading to the poor performance of lithium-ion batteries at cold temperatures are still not well understood.

Now, researchers at the Department of Energy’s SLAC National Accelerator Laboratory have shed light on the issue. Storing lithium-ion batteries at below-freezing temperatures can crack some parts of the battery and separate them from surrounding materials, reducing their electric storage capacity.

The researchers are working to understand the effects of the extreme temperatures of distant planets – or Midwest winters – on the rechargeable batteries that power devices like the Ingenuity Mars drone.

They discovered this problem analyzing the cold-weather performance of the cathode, the part of the battery electrons flow into when it’s in use. The previous studies have shown that storing cathodes at temperatures below zero degrees Celsius led batteries to lose up to 5% more of their capacity after 100 charges than batteries stored at warmer temperatures.

To comprehend the reason behind this, the researchers combined X-ray analysis methods at SLAC’s Stanford Synchrotron Radiation Lightsource with machine learning techniques. The combination allows them to identify individual cathode particles, allowing them to study thousands of particles at once, compared to just the handful they could identify with their eyes alone.

SLAC scientist Yijin Liu explained that the cold temperatures were shrinking the meatball-like particles within the cathode and, in the process, cracking them – or making existing cracks even worse. As the material differ in the way they expand and contract in response to changing temperatures, extreme cold was also detaching the cathodes from surrounding materials.

The results point to some possible fixes to improve the battery performance. Scientists could address the detachment issue by looking for battery materials that are better matched in terms of their temperature response. According to the researchers, this could also help improve the performance of other batteries as well, since all batteries expand and contract as they heat up and cool down. By engineering different particle structures inside a battery – notably, building them up from smoother, less meatball-like particles – researchers could help prevent cracking and improve long-term lithium-ion battery capacity.

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