Introducing...the Eco-Battery

It all started with a "simple" request to Johns Hopkins from the U.S. Air Force: create a lightweight all-polymer battery that can be molded into just about any size and shape for use in military equipment and satellites. Five years later, researchers unveiled what is now commonly known as "the plastic battery." The project was initiated and funded by Rome Laboratory, an Air Force research and development center in upstate New York. Materials science and engineering professors Theodore Poehler and Peter Searson guided the research team at Homewood, which included graduate student Jeffrey Killian, postdoctoral fellow Hari Sarker, and associate research scientist Jossef Gofer.

Most polymers that conduct electricity lack the necessary energy difference to act as charge storage electrodes. Yet the team persevered and used a combination of organic compounds to develop a practical battery in which the electrodes and the electrolytes are made of polymers--a first in this type of research. The plastic battery can generate up to 2.5 volts, which makes it potentially competitive with the 3-volt lithium batteries currently on the market. Further tests of the battery indicate that it can be recharged and reused hundreds of times. It has even more advantages, especially as a "green" battery. All-polymer batteries contain no heavy metals as their nickel-cadmium rechargeable counterparts do, so they will not contaminate groundwater and soil. Also, the batteries do not use liquids, which can present safety hazards if leaked.

Made up of two foil-like plastic sheets (the electrodes) with a polymer gel film (the electrolyte) between them, the highly adaptable battery can be as thin as a business card or thicker and larger to accommodate power-intensive applications. Because the battery itself is a sheet, it can be configured to fit any need. "You can imagine using it in a large sheet form, so that you could have a battery that occupied an entire wall...or you could roll it up into a tube, like AA-size batteries," says Searson. The group successfully demonstrated the feasibility of the technology, yet refinements are necessary before commercialization will be practical. The Hopkins team has applied for patents and talked to battery manufacturers who are interested in developing the plastic battery technology. It isn't hard to believe that, in a few years, the familiar pink bunny with the drum might have some real competition.

When Glass Isn't Glass

Todd Hufnagel, assistant professor of materials science and engineering, describes himself as a metallurgist interested in the novel materials known as metallic glasses. He explains: "In most metals, the atoms are arranged in a lattice--their positions are extremely well-defined, so much so that a particular metal's properties are determined as much by defects in the structure as the structure itself. A metallic glass, in contrast, is similar to window glass in that its atoms are not regularly arranged. This gives metallic glasses unique properties.

Fifty years ago, scientists thought it was impossible to create an amorphous metal. "In the 1950s, Cal Tech succeeded in making the first metallic glass," Hufnagel says. The trick was to cool the metal quickly--as fast as a million degrees Celsius per second--to prevent the lattice from forming. Over the last five to seven years, we have learned to make metallic glasses at cooling rates as low as one degree per second."

In his research, Hufnagel examines two aspects of these hybrid alloys. There is a limit to making metallic glass because of its tendency to crystallize. The glass forming alloys are very complex, with four or five different--and sometimes toxic--components. The rate at which such complicated alloys crystallize is not very well understood. Hufnagel uses x-ray diffraction techniques to study the structure of the alloys as they crystallize. "We can cool the alloy rapidly, then hold it at one point for analysis," Hufnagel says, "or we can cool it slowly and map what's happening gradually." Each step of the crystallization process has its own fingerprint, which allows him to measure the size of particles and their composition as they grow. The results of this research will aid in developing better alloys and in improving the manufacturing process.

In addition, Hufnagel is studying the mechanical properties of metallic glass after it cools. "I want to learn more about strength, ductility, and deformation," he says. "Currently we don't have a good understanding of the behavior of metallic glass at the atomic scale."

The potential of these materials is only limited by imagination. Metallic glasses can be much stronger than conventional alloys, they can have very useful magnetic properties, and they can withstand more deformation than crystalline materials. In fact, a California company is making a line of golf club heads out of the novel amorphous materials.