Self-Assembling Batteries

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The researchers used lithium cobalt oxide and microbeads of graphite for the electrodes--materials commonly used in lithium-ion batteries--pairing them with a carefully selected liquid electrolyte. The electrolyte serves as an insulator, allowing ions to shuttle between the electrodes but forcing electrons to move through an external circuit, where they can be used to power a device.

In the researchers' prototype battery, the graphite microbeads pack together to form one electrode and connect to a platinum current collector, all the while staying clear of the lithium cobalt oxide that forms the other electrode. The researchers tested the battery and showed that it could be both discharged and recharged multiple times.

The extent to which such batteries will find commercial applications is unclear. Dahn points out that in manufacturing today's batteries, the electrode materials are compressed under enormous pressures to ensure as great as possible energy storage. Such forces could not be applied to a self-assembled battery, so Dahn says it will be "very tough" to compete with conventional batteries in terms of energy capacity and maybe even in terms of cost. Dahn also notes that challenges still remain before such batteries can be commercialized. For example, it is still necessary to find a way to package the self-assembled materials to protect them once they have formed a battery.

One potential application is in very small devices. "It should be relatively easy to make a very small footprint device, rice-grain-size and smaller--the size of the head of a pin," Chiang says. He adds that self-assembly could allow more-efficient use of space than conventional batteries can. That's in part because it's possible for the electrode particles to pack into irregular shapes within a device or follow its outside contours.

As the researchers move toward such applications, which could include use in distributed sensors for the military, their next step is to replace the liquid electrolyte with a solid polymer to make the battery more rugged. The better understanding of the relevant short-range forces could also be used to select different materials for applications in transistors or certain types of solar cells.