April 23, 2009 Be they biological or computer, viruses generally get a pretty bad rap - what with their reputation for infection, reproduction and disease, it’s not surprising that their name is actually Latin for toxin or poison. But it's not all bad press - for example geneticists harness viruses to further the study of cell biology and they also hold much potential in the emerging field of nanotechnology where their size, shape and well-defined chemical structure has led to them being used as templates for organizing materials on the nanoscale. Now MIT researchers have turned viruses to the task of building a battery – and they’ve succeeded.
Using a virus that infects bacteria but is harmless to humans known as a bacteriaphage, the team were able to show it is possible to build both the positively and negatively charged ends of a lithium-ion battery using genetically engineered viruses. According to Angela Belcher, the MIT materials scientist who led the research team, the resultant virus-produced batteries have the same energy capacity as state-of-the-art rechargeable batteries being considered to power plug-in hybrid cars, and they could also be used to power a range of personal electronic devices.The benefits of this process is that it's both cheap and green, since it takes place at or below room temperature in an environmentally benign process that requires no harmful organic solvents and no toxic materials.
In standard lithium-ion batteries a lithium ion moves from a negatively charged anode to a positively charged cathode during discharge with that process reversed during charging. The most popular material used for the anode is graphite, but three years ago the 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. That breakthrough took the team two years, but solving the problem of how to use viruses to build a highly powerful cathode to pair up with the anode would take the team almost another three years. This was because cathodes are more difficult to build than anodes due to the fact that they must be highly conducting, but most candidate materials are highly insulating.
The answer for the team lay in genetically engineering viruses that first coat themselves with iron phosphate, then grab hold of carbon nanotubes to create a network of highly conductive material. The viruses recognize and bind specifically to the carbon nanotubes so that each iron phosphate nanowire can be electrically "wired" to conducting 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 team found that this method increased the cathode’s conductivity without adding too much weight to the battery. Lab tests showed that batteries using the new cathode could be charged and discharged at least 100 times without losing any capacitance. Although this is lower than then over 1000 charge cycles currently available in lithium-ion batteries Belcher says, "we expect them to be able to go much longer."
Although the prototype 3-volt battery produced by the team is packaged as a typical coin cell battery, the team says the technology allows for the assembly of very lightweight, flexible and conformable batteries that can take the shape of their container.
Now that the team has proven they can wire virus batteries at the nanoscale, they intend to pursue even better batteries using materials with higher voltage and capacitance, such as manganese phosphate and nickel phosphate. This next generation of the technology will have the potential to go into commercial production.
The virus-built batteries were detailed in a paper published in the April edition of Science and the battery was also presented at a press briefing at the White House where MIT President Susan Hockfield and President Barack Obama spoke about the need for Federal funding to advance new clean-energy technologies.
Source: MIT news
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