Innovation Pipeline

New thinking about how to design and build batteries is generating some novel research well outside the box of mainstream electronics. A group of scientists from the National Institute of Standards and Technology and Yale University recently revealed in a research paper in Advanced Materials how certain real cells generate electric voltages and hence act as a tiny battery.

Think about electric eels and how they manage to pack a lethal charge for their prey. The biological model offers an elegant alternative to conventional solid-state batteries.

Here’s how the researchers built their synthetic bio-battery cell. They started by creating a synthetic cell using a drop of water with salt, potassium and chloride ions. That droplet was then enclosed in fat, lipids walls. The lipid molecule at one end is attracted to water molecules while at the other end repels them. They inserted into the lipid sandwich layer a modified protein, alpha-hemolysin. These proteins create pores that act as channels for ions, which permits the passage of positive and negative ions through the lipid layers, thus creating voltage.

For now, the challenges are significant when it comes to building complex cells to create a microbattery. But researchers were able to build a battery made up of 11 microliters that lasted four hours. The battery lagged conventional lead-acid batteries: it was only about a 20th as effective, yet it was on par with conventional batteries when it came to conversion of chemical into electrical energy, at about 10 percent.

As one can see, batteries are moving in all sorts of new directions.

In another research effort, reported in the American Chemical Society’s Nano Letters, scientists at Uppsala University in Sweden are building batteries of paper and nonmetal parts. These ecofriendly batteries use conductive polymers. The underlying strength of the batteries is a nano-thin coating of polypyrrole that can be layered onto cellulose fibers of paper.

The Uppsala battery is capable of recharging faster than conventional rechargeable batteries because of its large surface area. Researchers used special cellulose, extracted from a certain species of green algae, with 100 times the surface area of cellulose found in paper.

This approach works best in applications that require rechargeable batteries that are flexible, such as in clothing or packaging.

In another effort, researchers at the University of Pennsylvania have demonstrated that the positive electrical charges of calcium ions can form bridges between negatively charged polymers that would normally repel each other. The polymers, like those of a living cell, with its lipid membranes, have a water-loving part linked to a water-repelling part. Calcium ions create calcium-rich islands, or patches, on top of negatively charged polymer. Researchers are designing materials at the nanoscale for future medical therapies wherein drugs can be wrapped within these polymer sacks, thus creating tiny biomedical sensors. By Lee Bruno