Virus builds both ends of battery

MIT researchers have shown they can genetically engineer viruses to build both the positively and negatively charged ends of a lithium-ion battery.

The new virus-produced batteries have the same energy capacity and power performance as rechargeable batteries being considered to power plug-in hybrid cars, and they could also be used to power a range of personal electronic devices, according to Angela Belcher, the MIT materials scientist who led the research team.

The new batteries, described in the April 2 online edition of Science, could be manufactured with a cheap and environmentally benign process: the synthesis takes place at and below room temperature and requires no harmful organic solvents.

Three years ago, an MIT team led by Belcher reported that it had engineered viruses that could build an anode by coating themselves with cobalt oxide and gold and self-assembling to form a nanowire.

In the latest work, the team focused on building a powerful cathode to pair up with the anode. Cathodes are more difficult to build than anodes because they must be highly conducting to act as fast electrodes. However, most candidate materials for cathodes are highly insulating.

To achieve that, the researchers genetically engineered viruses that first coat themselves with iron phosphate, then grab hold of carbon nanotubes to create a network of highly conductive material.

Because the viruses recognise and bind specifically to certain materials such as carbon nanotubes in this case, each iron phosphate nanowire can be electrically ‘wired’ to conducting carbon nanotube networks. Electrons can travel along the carbon nanotube networks, percolating throughout the electrodes to the iron phosphate and transferring energy in a very short time.

The viruses infect bacteria but are harmless to humans. The team found that incorporating carbon nanotubes increases the cathode's conductivity without adding too much weight to the battery. In lab tests, batteries with the new cathode material could be charged and discharged at least 100 times without losing any capacitance. That is fewer charge cycles than currently available lithium-ion batteries, but “we expect them to be able to go much longer”, Belcher said.

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