EV super-battery could be graphene's latest trick

Posted by Pete Danko, EarthTechling

Elon Musk has said the big breakthrough in electric vehicle energy may arrive with improved supercapacitors, not batteries.

At Rensselaer Polytechnic Institute, they're thinking precisely the opposite. Rensselaer researchers report using blemished graphene paper to create easy-to-make, quick-charging lithium-ion batteries with such high power density, they would render supercapacitors unnecessary.

"Li-ion battery technology is magnificent, but truly hampered by its limited power density and its inability to quickly accept or discharge large amounts of energy. By using our defect-engineered graphene paper in the battery architecture, I think we can help overcome this limitation," Nikhil Koratkar, a professor of engineering at Rensselaer, said in a statement.

A key thing to keep in mind here is the distinction between energy density and power density. Energy density is the amount of energy stored per unit of mass; power density is the maximum amount of power that can be supplied per unit of mass.

Lithium-ion batteries are high in energy density, but low in power density. As Rensselaer notes, "This low power density is why it takes about an hour to charge your mobile phone or laptop battery, and why electric automobile engines cannot rely on batteries alone and require a supercapacitor for high-power functions such as acceleration and braking."

Some – like Musk – have imagined that improvements in the energy density of the faster charging and discharging supercapacitors – potential improvements like using spongy carbon — could minimize the role of batteries. After all, if supercapacitors had high energy density to go along with their power density, what would be the point of batteries?  The far superior cycle life alone would make them a winner.

But by using doctored graphene paper, the Rensselaer team says, the battery part of the puzzle might win out. After all, the researchers say, anodes using their graphene material result in charging and discharging that's 10 times faster than the conventional graphite anodes used in today's li-ion batteries.

Ironically, it took damaging the graphene paper to make this work. The scientists did this by exposing the paper to either a laser or "a simple flash from a digital camera" (really!), and in both cases "mini-explosions" from the heat left the graphene "pockmarked with countless cracks, pores, voids and other blemishes."

The result was that when used as the anode material for the lithium-ion battery, instead of having to work their way across the length of the layers of graphene to enter or exit the battery's anode from the edges, "the ions now used the cracks and pores as shortcuts to move quickly into or out of the graphene—greatly increasing the battery's overall power density."

Koratkar sounds extremely optimistic about the possibility of this technique making its way from his lab to industrial use.

"We believe this discovery is ripe for commercialization, and can make a significant impact on the development of new batteries and electrical systems for electric automobiles and portable electronics applications," he said.

The university said the researchers have filed for patent protection for their discovery. Meanwhile, they'll now go to work on pairing the graphene anode material with a high-power cathode material to construct a full battery.

* Pete Danko, EarthTechling