MIT Explores A Lithium Iron Phosphate Battery From the Inside
Researchers at Massachusetts Institute of Technology recently announced a new finding on long cycle life and high power of lithium iron phosphate (LiFePO4) cells.
“The MIT researchers found that inside this electrode, during charging, a solid-solution zone (SSZ) forms at the boundary between lithium-rich and lithium-depleted areas — the region where charging activity is concentrated, as lithium ions are pulled out of the electrode.”
Such mechanism was theoretically predicted, but according to the paper in the journal Nano Letters (by MIT postdoc Jun Jie Niu, research scientist Akihiro Kushima, professors Yet-Ming Chiang and Ju Li, and three others), for the very first time SSZ were seen directly in transmission electron microscope (TEM) videos taken during charging.
Will this help researcher and manufacturers to build better batteries? Probably yes because now a better understanding of dynamic processes enable further optimization of electrode material.
“The observations help to resolve a longstanding puzzle about LiFePO4: In bulk crystal form, both lithium iron phosphate and iron phosphate (FePO4, which is left behind as lithium ions migrate out of the material during charging) have very poor ionic and electrical conductivities. Yet when treated — with doping and carbon coating — and used as nanoparticles in a battery, the material exhibits an impressively high charging rate.”
“The SSZ is a “metastable” state, persisting for at least several minutes at room temperature. Replacing a sharp interface between LiFePO4 and FePO4 that has been shown to contain many additional line defects called “dislocations,” the SSZ serves as a buffer, reducing the number of dislocations that would otherwise move with the electrochemical reaction front.”
Ju Li, the Battelle Energy Alliance Professor of Nuclear Science and Engineering and a professor of materials science and engineering, stated:
“We directly observed a metastable random solid solution that may resolve this fundamental problem that has intrigued [materials scientists] for many years.”
These findings were possible due to special a TEM imaging technique developed by Ju Li and Akihiro Kushima in 2010.
“Unlike conventional TEM imaging, the technique used in this work, developed in 2010 by Kushima and Li, makes it possible to observe battery components as they charge and discharge, which can reveal dynamic processes.”
“In the last four years, there has been a big explosion of using such in situ TEM techniques to study battery operations.”