Experts Figure Out How Key Li-Ion Battery Material Works

August 15, 2011 - via

A group of investigators at the Massachusetts Institute of Technology (MIT) and the University of California in Los Angeles (UCLA) managed to understand why a material widely used for creating lithium-ion batteries actually works.

Up until now, lithium iron phosphate (LiFePO4) has been heavily used to produce the positive electrode (cathode) of Li-Ion batteries, but experts had no idea why it worked the way it did.

The reason for this is the fact that theories on the behavior this material should display indicate it should require a two-phase process to store lithium. This naturally led scientists to believe that these cathodes' efficiency levels should decrease.

However, this was not observed. In fact, the material functions better than any other used in Li-Ion batteries. What the MIT/UCLA team did was find the reason why this compound is so efficient.

In order to understand what the researchers did, it's important to remember that cathodes are responsible for storing electricity, and that they are characterized by two critically-important measures – its energy and power density.

The first measure refers to how much electricity a cathode of a certain weight can hold, while the second one refers to the time they need to release all that stored energy. The higher these values, the more efficient a battery becomes.

When recharged, batteries essentially eliminate lithium ions from the cathode, replacing them with lithium atoms. It's here that LiFePO4 should have needed two steps to recharge the cathode, but didn't.

The investigators determined that in fact the theories were wrong. The compound recharged the cathode in a single step, but went about doing this in an interesting, unusual manner. The study also reveals the possibility that other, similar materials may be found, or produced artificially.

The research team was made by the MIT Richard P. Simmons professor of materials Science and engineering Gerbrand Ceder and graduate student Rahul Malik, alongside UCLA postdoctoral researcher Fei Zhou.

Details of the research appear in the latest issue of the top scientific journal Nature Materials.

The “authors make a strong case that the solid solution phase plays a bigger role in the performance [the compound displays]. […] the work suggests alternative directions to the design of cathode materials for lithium batteries,” Brent Fultz explains.

The California Institute of Technology (Caltech) professor of materials science and applied physics was not involved in the new study.

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