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Graphene paper anodes pave way for faster charging Li-ion batteries

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August 27, 2012

A scanning electron microscope image of the treated graphene oxide paper

A scanning electron microscope image of the treated graphene oxide paper

While the lithium-ion batteries commonly used in electric cars are capable of storing a fairly large amount of energy, they’re not able to accept or discharge that energy very quickly. That’s why electric vehicles require supercapacitors, to speedily deliver energy when accelerating, or to store it when braking. Recently, however, researchers from New York’s Rensselaer Polytechnic Institute created a new anode material, that allows Li-ion batteries to charge and discharge ten times faster than those using regular graphite anodes. It could make EV supercapacitors unnecessary, and vastly shorten the charging time required by electronic devices.

The team, led by Prof. Nikhil Koratkar, started by creating a large sheet of graphene oxide paper. About the thickness of a piece of printer paper, it was made up of layered sheets of graphene (each graphene sheet being composed of a one one-atom thick layer of linked carbon atoms).

That paper was cut into smaller pieces, which were then subjected either to a laser, or the flash from a compact camera. In either case, the resulting flash of heat caused “mini explosions” to take place throughout the thickness of the paper, as oxygen atoms were expelled from its structure. The result of this carnage was graphene sheets that were full of flaws such as cracks, pores and voids. Additionally, the pressure exerted by the escaping oxygen forced the stacked layers of graphene apart from one another, resulting in a five-fold increase in the thickness of the paper.

When samples of this paper were tested for use as anodes, however, the marked decrease in charge and discharge times was noted. This was due to the fact that the lithium ions could enter (or exit) the anode at almost any point, using its imperfections as points of entry – by contrast, on graphite anodes, the ions can only enter at the sides and then slowly work their way into the middle.

The graphene oxide paper anodes were found to still work perfectly after more than 1,000 charge/discharge cycles. According to Koratkar, the sheets can be easily and inexpensively made in just about any shape or size, and the production process should be easy to scale up. His team’s next order of business is to match the anodes up with a high-power cathode, within a full Li-ion battery.

A paper on the research was recently published in the journal ACS Nano.

Source: Rensselaer Polytechnic Institute

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.   All articles by Ben Coxworth
3 Comments

Li-ons charge speed is not the problem, it is the 2 year lifespan of Lithium batteries.

L1ma
28th August, 2012 @ 09:14 am PDT

'While the lithium-ion batteries commonly used in electric cars are capable of storing a fairly large amount of energy, they’re not able to accept or discharge that energy very quickly. That’s why electric vehicles require supercapacitors, to speedily deliver energy when accelerating, or to store it when braking.'

Their starting words are a lie so I suspect the rest is likely hype. There are many batteries that can put out too much current. We, EVer's have 400vdc, 2,000 amp Li-ion packs. That's about 800hp in 150lbs!!! Just look up Killacycle.

Ultra caps are by far the most overpriced, overhyped close to useless thing out there. They cost 50-100x's as much as lithium A-123's for the same output. Nor does anyone mention the electronics needed to make UC's work because of their decreasing voltage.

jerryd
28th August, 2012 @ 10:04 am PDT

I think the speed of charge/discharge is related to the life of the battery. Batteries are complicated devices. A lot was unsaid in this short article. Probably reducing the resistance of the anode and improving access for the lithium ions does several things. Reducing internal resistance cuts down on internal heating of the battery. Heat causes all sorts of problems. Also, reducing internal resistance increases available power. Improving access for the lithium ions probably reduces the likelihood of unwanted chemical changes near the anode when potentials build up and the ions can't move fast enough to counter that. You may recall an announcement a few years ago that lead acid batteries could be charged much faster by pulses of current. The short periods between pulses allowed time for the electrolytes to return to equilibrium in the vicinity of the battery plates.

1,000 charge cycles implies a three year life if you assume one charge/discharge per day.

neutrino23
1st September, 2012 @ 10:32 pm PDT
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