Nature is a far better builder than man, especially when things get very small. Biology, for example, has evolved molecule-by-molecule assembly tricks that engineers, even with billions of dollars worth of exotic equipment, can't equal.
As technology continues to shrink, scientists are looking to nature's tool kit to make the next generation of high-performance materials. In an example of this shift, scientists at the Massachusetts Institute of Technology have customized a benign virus to act as the building block for an advanced battery material that couldn't be made using conventional methods.
The resulting material looks like clear, sticky tape. But it is the first component in a new kind of battery with the potential to create rechargeable batteries that could last two or more times as long as those available for today's wireless phones and notebook computers, says Yet-Ming Chiang, a materials scientist. Chiang is also co-author of a paper describing the new process and material published in the Apr. 7 issue of the journal Science. Plus, because it's flexible and reasonably durable, the material could be made into tiny batteries to power ultra-small devices or layered into the case or other structural components of an electronics device. "Or, since it's transparent, it could be even laid over a display," he says.
NO ASSEMBLY REQUIRED. Remarkable as it promises to be, how the material was made may spark a bigger bang -- or even mark the dawn of an era of clean, fast "molecular self-assembly. In MIT's recipe, a virus was bred so that its coat would attract key chemicals. Once multiplied in the lab, a batch of the virus strands were then exposed to those chemicals: a special mix of cobalt oxide and gold molecules chosen for their efficiency as battery media. In the last step, the metal-coated viral strands were laid out on a thin, clear, electrically charged polymer sheet.
Next, comes the magic of nature. Thanks to a slight electrical charge the viruses carry, they arrange themselves into an orderly, nonoverlapping layer of strands just 6 nanometers thick -- about 1/10,000th the width of a human hair. "This could only be done through self-assembly," explains Angela Belcher, a co-author of the paper and a materials and biological engineer.
The advantages of this approach show the promise of self-assembly. Belcher's recipe was assembled at room temperature, on a lab counter, using a modicum of energy. Processes such as these "evolved in nature to work at room temperature, with no toxins," says Belcher. If we can harness them to help assemble new materials, she suggests, they will disrupt long-stand manufacturing methods.
MISSING PIECES. By contrast, today's lithium-ion batteries are made in a series of complex steps typical of advanced manufacturing. Ovens heat toxic powders to very high temperatures. Rolls of ultra-thin metal foil are coated with the power and folded by advanced devices into structures that store energy.
What's next? "Well, don't expect to replace your notebook battery anytime soon," jokes Chiang. The publication of the steps to create this transparent battery film represents a proof of process, not a final product. For now, the team has perfected just the anode -- the negative side of a battery from which electrons flow. Still to be completed, says Chiang, are the recipes to grow a current collector (a midlayer that will draw the power out) and a cathode (the positive half of the battery) on the other side of the film.
Whatever the recipe, the MIT researchers are confident self-assembly will make it easier to take this next-generation battery from lab to market.