Can graphene, the wonder material, build better batteries?
In 1962, German researcher Hanns-Peter Boehm suggested the versatile carbon atom, which can form long chains, might be configured into a chicken-wire pattern to create a stable molecule one atom thick.
The idea remained a theoretical construct without even a name until 1987, when researchers started calling it “graphene.” Basically, graphene is two-dimensional graphite, the pure carbon material that makes up “lead” pencils. The term was also used to describe the carbon nanotubes that were beginning to attract attention for their ultra-solid properties. For a while there was talk of elevators reaching up into space until it became clear that creating nanotubes without impurities that degrade their properties was currently out of the reach of mass production.
Then in 2004, Andre Geim and Kostya Novoselov, two researchers at The University of Manchester, came up with something a little more prosaic. They applied Scotch tape – yes, ordinary Scotch tape – to pure graphite and found they could peel off the single layer of carbon in the chicken-wire pattern that Boehm had described. They called this substance “graphene” and were awarded the Nobel Prize in 2010.
The discovery of single-layer graphene has set off a stampede into research of its properties. Carbon is, after all, a versatile element, the basic building block of life that can also be packed into a material as hard as a diamond, which is also pure carbon. When stretched out into lattices a million times thinner than a human hair, however, it has the following remarkable properties:
- It is the strongest material ever discovered, 300 times stronger than steel.
- It is the most electrically conductive material ever discovered, 1,000 times more conductive than silicon.
- It is the most thermally conductive material ever discovered.
- It is bendable, shapeable and foldable.
- It is completely transparent, although it does filter some light.
In short, graphene is now being touted as “material of the 21st century,” the substance that could bring us into an entirely new world of consumer products, such as cell phones that could be sewn into our clothes.
All this still remained somewhat theoretical, since no one had been able to produce graphene in dimensions larger than single tiny crystals. When these crystals were joined together, they lost most of their properties. Two weeks ago, however, Samsung announced that it has been able to grow a graphene crystal to the size of a wafer, somewhat on the same dimensions as the silicon wafers that produce computer chips. Thus, the first step toward a new world of electronics may be upon us. Graphene cannot be used as a semiconductor, since it is always “on” in conducing electricity, but combined with other substances it may be able to replace silicon, which is many researches believe is currently reaching its physical limits.
So what does this mean for the world of transportation, where we are always looking for new ways to construct automobiles and find alternative power sources to substitute for our gas tanks? Well, plenty.
Most obvious is the possibility of making cars out of much lighter-weight materials to reduce the power burden on engines. Chinese researchers recently came up with a graphene aerogel that is seven times lighter than air. A layer spread across 28 football fields would weigh only one ounce and a cubic inch of the material would balance on a blade of grass. All this would occur while it still retained its 300-times-stronger-than-steel properties. Graphene itself would not be used to construct cars, but it could be layered with other materials.
But the most promising aspect of graphene may be in the improvement of batteries. Lithium-ion batteries achieve an energy density of 200 Watt-hours-per-kilogram, which is five times the 40-Wh/k density of traditionally lead-acid batteries. That has won it the prime role in consumer electronics. But Li-ion batteries degrade over time, which is not a problem for a cell phone, but becomes prohibitive when the battery must undergo more than 1,000 charge cycles and is half the price of the car.
Lithium-sulfur batteries have long been thought to hold promise but they, too, deteriorate quickly, sometimes after only a few dozen charges. But recently, researchers at Lawrence Berkeley Labs in California modified a lithium sulfur battery by adding sandwiched layers of a graphene. The result is a battery that achieves 400 Wh/k – double the density of plain lithium-ion – and has gone through 1,500 charging cycles without deterioration. This would give an electric car a range of more than 300 miles, which is in the lower range of what can be achieved with the internal combustion engine.
And so the effort to improve electric vehicles is moving forward, sometimes on things coming out of left field. If graphene really proves to be a miracle substance, look for Elon Musk to be discussing its wonders as he prepares to build that “megafactory” that is supposed to produce lithium-ion batteries capable of powering an affordable new version of the Tesla.