Thin Material Hikes EV Battery Power

Tuesday, February 24, 2015 @ 11:02 AM gHale

A paper-like material is now in development to make a stronger and more powerful lithium-ion battery.

This technology has the potential to boost by several times the specific energy, or amount of energy that can end up delivered per unit weight of the battery.

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This paper-like material consists of sponge-like silicon nanofibers more than 100 times thinner than human hair. It could see action in batteries for electric vehicles and personal electronics, said researchers at University of California, Riverside’s Bourns College of Engineering.

The nanofibers ended up produced using a technique known as electrospinning, where 20,000 to 40,000 volts go between a rotating drum and a nozzle, which emits a solution composed mainly of tetraethyl orthosilicate (TEOS), a chemical compound frequently used in the semiconductor industry. The nanofibers then end up exposed to magnesium vapor to produce the sponge-like silicon fiber structure.

Conventionally produced lithium-ion battery anodes end up made using copper foil coated with a mixture of graphite, a conductive additive, and a polymer binder. But, because the performance of graphite appears at its limit, researchers are experimenting with other materials, such as silicon, which has a specific capacity, or electrical charge per unit weight of the battery, nearly 10 times higher than graphite.

The problem with silicon is it suffers from significant volume expansion, which can quickly degrade the battery. The silicon nanofiber structure created in the lab of Mihri Ozkan, a professor of electrical and computer engineering at UC-Riverside and one of the authors of a paper on the subject, circumvents this issue and allows the battery to cycle hundreds of times without significant degradation.

“Eliminating the need for metal current collectors and inactive polymer binders while switching to an energy dense material such as silicon will significantly boost the range capabilities of electric vehicles,” said Zach Favors, a graduate student at UC-Riverside and one of the authors of a paper on the subject.

This technology also solves a problem that has plagued free-standing, or binderless, electrodes for years: Scalability. Free-standing materials grown using chemical vapor deposition, such as carbon nanotubes or silicon nanowires, can only end up produced in very small quantities (micrograms). However, Favors was able to produce several grams of silicon nanofibers at a time even at the lab scale.

The researchers’ future work involves implementing the silicon nanofibers into a pouch cell format lithium-ion battery, which is a larger scale battery format that can see use in EVs and portable electronics.



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