Shrunken rods make batteries better

Grow your own

A plastic polymer and an extremely hot oven are behind a research breakthrough that will see lithium batteries get a significant power boost.

The new technique allows researchers to grow miniature carbon pillars. These are used to build an array of terminals between which current can flow. The terminals would float in a sea of lithium ions, effectively multiplying the number of cells in a given amount of space.

Batteries like these will be able to generate larger bursts of current than conventional cells, and could also be wired to provide varying levels of power depending on demand, the researchers say.

The theory is not new but the researchers, based at the University of California, have developed a technique that can make the theory work in the real world. The problem was: how to grow the rods? Marc Madou, the team leader, told Nature. That breakthrough came from his colleague, Chimlei Wang.

Wang used a plastic polymer which hardens when it comes into contact with light, creating the rods by shining light onto the polymer surface through a "hole-y" mask. After etching away the unreacted polymer, the team baked the rods at 900°C in an oxygen-free atmosphere.

In the same way that 10-year-olds make key rings out of crisp packets by shrinking them in the oven, the rods shrink during the baking as the hydrogen and atoms within the polymer are burned off. Finding a substance that could survive the heat of the oven was the key step forward.

To complete the battery, Wang and Madou poured lithium ions into the space between the rods and wired lines of them together so that alternative rows acted as the positive and negative terminals of a battery.

Commercial deployment is still a way off. The technology used to grow the rods is silicon-based. The team says it will need to find a cheaper method before the batteries could compete in the open market. ®

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