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Over the past three decades, lithium-ion batteries, rechargeable batteries that move lithium ions to charge and discharge, have allowed smaller devices to recharge faster and last longer.
At present, the X-ray experiments conducted by the National Laboratory of SLAC Accelerators and the National Laboratory Lawrence Berkeley of the Ministry of Energy have revealed that the pathways taken by lithium ions through a common battery material are more complex than previously thought. The results correct more than two decades of assumptions about the material and will help improve the design of batteries, which could lead to a new generation of lithium-ion batteries.
An international team of researchers led by William Chueh, a Stanford Institute of Materials Science and Materials Researcher at SLAC and a professor of materials science at Stanford, published these results today in: Nature Materials.
"Before, it was a bit like a black box," said Martin Bazant, a professor at the Massachusetts Institute of Technology and another leader of the study. "We could see that the material worked quite well and that some additives seemed to help, but we could not say exactly where the lithium ions went at each stage of the process. You can only try to develop a theory and work from measurements. With new instruments and measurement techniques, we begin to have a more rigorous scientific understanding of how these things really work. "
The "popcorn" effect
Anyone who has used a power tool or a cordless vacuum cleaner in an electric bus has probably benefited from the advantages of the studied battery material, iron phosphate and lithium. It can also be used for start and stop function in cars equipped with internal combustion engines and for storage of wind and solar energy in power grids. A better understanding of this material and other similar materials could lead to faster, more durable and more durable charge batteries. But until recently, researchers could only guess the mechanisms that make it work.
When lithium-ion batteries charge and discharge, lithium ions flow from a liquid solution into a solid reservoir. But once in the solid, lithium can reorganize itself, sometimes causing the material to separate into two distinct phases, much like oil and water separate when mixed. This causes what Chueh calls "a popcorn effect". The ions cluster in hot spots that eventually shorten the life of the battery.
In this study, researchers used two x-ray techniques to explore the inner workings of lithium-ion batteries. At SLAC's Stanford Synchrotron Radiation Station (SSRL), they returned X-rays of a sample of iron and lithium phosphate to reveal its atomic and electronic structure, giving them an idea of how lithium ions were moving in the material. Thanks to Berkeley Lab's Advanced Light Source (ALS), they used X-ray microscopy to magnify the process, thus allowing them to map the evolution of lithium concentration over time.
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