Materials Design at the Intersection of Nanotechnology and Energy

This intracellular landscape is punctuated by mitochondria (purple), power plants that might be harnessed, one day, as a source of hydrogen for engineered devices. (Art by Chris Burke, University of Michigan)

Twenty pounds. On average, that’s how much coal it takes to generate the electricity that each person in the United States uses every day.  That’s a lot of coal, and although it produces more than half the electricity in the United States, it also puts out 40 percent of the country’s carbon dioxide emissions. Oil’s a dirty fuel, too, as well as costly and politically destabilizing – of 100 foreign policy and national security experts surveyed by the Center for American Progress and Foreign Policy, 86 percent said the world is “becoming more, not less, dangerous for Americans, and foreign oil is probably the single most pressing priority in winning the war on terror.”

Natural gas is an up-and-coming alternative fuel, but it’s expensive and, unlike oil, hard (and costly) to transport. Ethane and hydrogen have potential, but they’re hard to store.

Finding an efficient, clean, abundant source of energy is a major challenge, one that’ll become more critical as time goes on – the world’s energy demands will more than double by the year 2050.  

Michigan Engineering’s Ann Marie Sastry is attacking the energy problem from a number of angles, one of which is the development of efficient, compact, lightweight  batteries with a long shelf life, better storage capacity than existing batteries, little impact on the environment, and enough power for applications in defense, industry, healthcare and consumer electronics.

Sastry, a professor with appointments in the departments of Mechanical Engineering, Biomedical Engineering, and Materials Science and Engineering, is designing carbon particles that are about one-billionth of a meter across and, when shaped and packed together properly in clusters, conduct electricity. One of the many obstacles she faces is working on particles at the nanoscale.

“The easy transport problems have been solved, for spheres and other regular shapes,” Sastry said, “but to work with millions of particles, with choices range from platelets to fibers to spheroids, we’ve developed new mathematical techniques, to understand connectivity, and how these power materials will behave in practice.”

In power sources ranging from tiny, implantable batteries to automotive batteries in hybrid vehicles, size constraints are key. Sastry said that in designing smaller power supplies she has to “make the best use of volume and mass we have – since you don’t want to spend all of the energy you’re putting on board, to carry around a heavy power supply.”

Sastry went on to say, “Imagine electrons zinging around in an electrode. We have to create intricate highways out of nanoscale particles to make sure that charge density is evenly distributed, the highways draw current and we get all possible capacity out of the cell. That means we have to make sure that particles that conduct electrons connect but don’t add too much mass. Stretching out the particles creates longer connection lengths using less mass, so that’s why we often design materials with fibers – and why understanding percolation in multiphase materials is so important.” (Percolation is the formation of continuous pathways for transport in a material.)

Sastry’s modeling technique requires large, complex computations. This poses yet another problem: In doing large calculations, small errors lead to huge mistakes. “But compared with experimentation,” she said, “calculations offer a fast and inexpensive way to explore many possibilities. And we’d like try out a new technology on a computer a million times, and test just a few of them, rather than just burn up a million units in the lab. Frankly, with pressing environmental needs, we can’t afford to waste time or money, in getting materials out of the lab and into cars.”

The material designs that Sastry is creating now at the nanoscale are an important step toward the creation of environmentally friendly and sustainable global power supplies. More specifically, her designs will play a critical role in the replacement of gas-burning cars with clean vehicles, providing energy storage for use in hybrid grid sources with photovoltaics and wind power, and powering microelectronics without adding bulk. These efforts are an integral part of a University of Michigan initiative that quite literally has the potential to revolutionize energy sources – from polluting and unsustainable sources, to clean energy technologies.