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Too many electrons at the lithiation front in silicon are a problem

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Posted March 10, 2014
Too many electrons at the lithiation front in silicon are a problem
Molecular simulations and experiments show the initial structure of the lithium silicon alloy and the amorphization that occurs after 420 femtoseconds. The lithium ions are the red spheres and the silicon atoms are the green spheres.
Ubiquitous but frustrating, lithium-ion batteries fade because the materials lose their structure in response to charging and discharging. This structural change is closely related to the formation of electron-rich regions within the electrode, according to scientists at Pacific Northwest National Laboratory (PNNL), the University of Electronic Science and Technology of China, Northwestern University, and Rensselaer Polytechnic Institute. The team used experiments and molecular simulations to show that the electron-rich region causes silicon bonds to break. The bond breakage transforms crystalline silicon into an amorphous alloy of lithium and silicon.

“It was absolutely unclear what was going on, although a lot of papers described how inserting lithium ions into materials leads to amorphization,” said Dr. Fei Gao, a chemical physicist and a corresponding author on the study. “We propose that local electron-rich conditions induce amorphization.”

As every owner of a mobile phone knows, lithium-ion batteries fade, storing less energy each time they are charged. Over time, a battery declines to the point that it has to be replaced, at both an environmental and financial cost.

Read more at: Phys.org

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