Graphene and green tech

graphene-and-green-tech

It was just one of their Friday night experiments, nothing out of the ordinary. Then Andre Geim and Konstantin
Novoselov made a discovery that would change the world of engineering forever. It was simple: they used sticky tape to remove the top layer from a chunk of graphite. Many had done it before them but none had quite realised what was stuck to the tape. What they had isolated was graphene.

Ten years on and graphene’s potentials are unbounded. From applications in touchscreen devices to possible uses as a cancer therapy, the material is changing the world before our very eyes. Now graphene promises to transform energy storage, which has been left behind in recent years despite a surge of technological advances. A number of problems still exist for this technology: batteries and capacitors are often bulky, heavy, have low energy capacity and long charging times.

For electric vehicles these issues equate to a reduction in efficiency and hence a barrier to their widespread uptake. Energy storage for renewables is also difficult. Since high winds don’t always coincide with high electricity demands we need cheap batteries that can be used to store energy when the wind is blowing and release it when everyone needs it. Then perhaps renewables would start to look like a more attractive option.  

Now researchers at the University of Manchester and the University of Liverpool have begun a new project to investigate the possibility of using graphene in these energy storage devices.

The material boasts numerous qualities that make it fit for the job, which all stem from the fact that it is a one-layer-thick honeycomb lattice of carbon atoms. This means it is extremely thin: at only 0.345 nanometres, graphene measures around 300,000 times thinner than a sheet of paper.

“The structure is so thin it makes the electronic bond structure more firm than any other material, so the fact that electrons can travel in graphene very fast and very efficiently makes graphene’s conductivity higher than anything else,” explains Cecilia Mattevi of the Department of Materials, Imperial College London.

It is also extraordinarily light: a sheet of graphene large enough to cover a whole football pitch would weigh just less than one gram. Combined with the fact that it is strong, flexible and an excellent electricity conductor, these properties mean that it could reduce the size and weight of batteries whilst also increasing efficiency.

“Every battery electrode has a little bit of sooty carbon in it, that’s the material they currently use, which sort of connects the particles and makes sure that electrons can percolate through the electrodes,” explains Laurence Hardwick of the University of Liverpool, one of the project’s lead researchers.

Hardwick and his colleagues are looking at whether graphene could replace the “sooty carbon” to increase conductivity. “So in principle could we make an electrode and thus a battery which can deliver more power because we can get the electrons in and out of the active materials much quicker,” says Hardwick.

Using graphene in batteries could also help tackle the problem of energy storage and charging times. The problem is that a battery has the power to hold a lot of energy but it can take a long time to charge. Conversely, capacitors can be charged quickly but don’t store much electricity. The challenge now is to develop a device that charges quickly and stores a large amount of energy without compromising on anything else.

This is where graphene comes in. Due to its bonding structure, this 2D material packs in more lithium ions per carbon atom than graphite can. Lithium is a highly reactive element, meaning it can store a huge amount of energy in its atomic bonds. Because of this, graphenic batteries have a much larger energy storage capacity than graphite batteries.

Incorporating a combination of graphenic batteries and super capacitors into electric vehicles could give them the extra boost they need. Currently, electric vehicles run on batteries that weigh some 200kg, around the weight of three passengers. But graphenic batteries could be much lighter.

“You could maybe get 20 or 30 per cent more power out of the battery,” says Hardwick. “So that sort of number, that maybe is not, say, a revolution but it’s more of a small step on the way of getting much better batteries.”

To investigate this further, the team will research how graphene interacts with lithium ions and test exactly how much energy can be stored on the graphenic surfaces. They will also need to assess whether graphenic batteries are up to the job by trialling them in weather chambers that mimic different driving conditions.

There’s still a long way to go before everyone drives electric vehicles charged with renewable energy, but like Hardwick says, graphene is taking us one step closer. We’re only ten years on from Geim and Novoselov’s Nobel prize-winning isolation of graphene, so who knows where the next ten years could take us. 

 

IMAGE: CORE-Materials

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