Golden Age For Materials by Cook & Bynum
The pace of innovation in materials science is leading to new commercial and consumer applications that will both change existing and perhaps birth new industries. For example, meaningful gains are being made in semiconductors and batteries, the latter being a topic that particularly interests us.
New, high-performing substances such as exotic alloys and superstrong composites are emerging; “smart” materials can remember their shape, repair themselves or assemble themselves into components. Little structures that change the way something responds to light or sound can be used to turn a material into a “metamaterial” with very different properties. Advocates of nanotechnology talk of building things atom by atom. The result is a flood of new substances and new ideas for ways of using them to make old things better—and new things which have never been made before…
The understanding of the material world provided by a century of physics and chemistry accounts for much of the ever-accelerating progress. But this is not a simple triumph of theory. Instruments matter too. Machines such as electron microscopes, atomic-force microscopes and X-ray synchrotrons allow scientists to measure and probe materials in much greater detail than has ever been possible before.
A project at the International Centre for Advanced Materials at the University of Manchester shows such advances in action. In one of its labs scientists are using secondary ion mass spectrometry (SIMS) to study the way that hydrogen atoms—the smallest atoms there are—diffuse into materials such as steel, a process that can cause tiny cracks. SIMS works by bombarding a sample with a beam of charged particles, which causes secondary particles to be ejected from the surface. These are measured by an array of detectors to create an image with a resolution down to 50 nanometres (billionths of a metre). It does not just reveal the crystalline structure of the metal—and any flaws in it—but also determines chemical impurities, such as the presence of hydrogen. “We can now do in an afternoon what we once did in months,” says Paul O’Brien, a professor at the university. The hope is that BP, the oil company which is sponsoring the centre, will get better steels for its offshore and processing work as a result.
As well as having ever better instruments, the researchers are also benefiting from a massive increase in available computing power. This allows them to explore in detail the properties of virtual materials before deciding whether to try and make something out of them. “We are coming out of an age where we were blind,” says Gerbrand Ceder, a battery expert at the University of California, Berkeley. Together with Kristin Persson, of the Lawrence Berkeley National Laboratory, Mr Ceder founded the Materials Project, an open-access venture using a cluster of supercomputers to compile the properties of all known and predicted compounds. The idea is that, instead of setting out to find a substance with the desired properties for a particular job, researchers will soon be able to define the properties they require and their computers will provide them with a list of suitable candidates.
Their starting point is that all materials are made of atoms. How each atom behaves depends on which chemical element it belongs to. The elements all have distinct chemical properties that depend on the structure of the clouds of electrons that make up the outer layers of their atoms. Sometimes an atom will pair off one of its electron with an electron from a neighbouring atom to form a “chemical bond”. These are the kind of connections that give structure to molecules and to some sorts of crystalline material, such as semiconductors. Other sorts of atom like to share their electrons more widely. In a metal the atoms share lots of electrons; there are no bonds (which makes metals malleable) and electric currents can run free.
When it comes to making chemical bonds, one element, carbon, is in a league of its own; a more or less infinite number of distinct molecules can be made from it. Chemists call these carbon-based molecules organic, and have devoted a whole branch of their subject—inorganic chemistry—to exploring them. Mr Ceder’s Materials Project sits in that inorganic domain. It has simulated some 60,000 materials, and five years from now should reach 100,000. This will provide what the people working on the project call the “materials genome”: a list of the basic properties—conductivity, hardness, elasticity, ability to absorb other chemicals and so on—of all the compounds anyone might think of. “In ten years someone doing materials design will have all these numbers available to them, and information about how materials will interact,” says Mr Ceder. “Before, none of this really existed. It was all trial and error.”
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One of the more important applications for engineering the microstructure of materials is in batteries. These have been made from various materials, such as lead-acid and nickel-cadmium. Apart from being highly toxic, some of these ingredients are also bulky and heavy, hence mobile phones in the 1980s were brick-like. The rechargeable lithium-ion battery helped slim them down…
Yet the search for a better battery is still on. For some applications, such as electric cars, this would be transformative. Until recently the battery for an electric car could cost $400-$500 per kilowatt hour, representing perhaps 30% or so of the overall cost of the vehicle, but costs are falling. In October General Motors said it expected the battery in its new Chevy Bolt electric car, due to go on sale in 2016, to cost around $145 per kilowatt hour. The industry believes that once the cost comes down to around $100 per kilowatt hour, electric vehicles will become mainstream because they will be able to compete with petrol cars of all sizes without subsidy…
Sakti3, however, has found a way to make a solid lithium battery with a thin-film deposition process, a technique already widely used to produce things such as solar panels and flat-panel display screens. “Solid-state technology will offer about double the energy density—that’s double the talk time on your phone; double the range in your electric car,” says Ann Marie Sastry, the firm’s chief executive. The battery cells will also have a long service life and be safer, she adds.
So why has the technique not been used to make batteries before? The firm’s purported edge is knowing what materials to use and how to make the process cost-effective. Everything, including the complicated physics, was worked out and extensively tested virtually before the company built a pilot production line. Ms Sastry explains that as the firm selected materials and developed processes, the virtual computer tests enabled it to forecast the cost of scaling up production. When built in large volumes, the solid-state batteries should come in around $100 per kilowatt hour, and there is scope for further improvement…
“I think batteries will change the world,” says Mr Ceder at Berkeley, “and that is purely a materials issue.” He has worked on nearly every battery technology, but lithium remains his favourite, not least because so much