The batteries are seen as a future way to power small electronic devices including cell phones and MP3 players as well as, eventually, much larger applications such as those in automobiles. Although the viruses infect bacteria, they are harmless to humans, according to MIT researchers. And being organic, they seem to be the pinnacle of environmentally friendly engineering.

The recent discovery was built upon research performed three years ago, when an MIT team reported that it had genetically engineered viruses that could build an anode by coating themselves with cobalt oxide and gold and self-assembling to form a nanowire. Traditional batteries have two anodes: The positive terminal (often cobalt oxide) and the negative one (graphite).

In the latest work, the team focused on building a highly powerful cathode to pair up with the anode. Because the cathode had to be highly conductive—but typically are made of insulating rather than conductive material—the scientists were faced with a significant challenge. In the end, the viruses were engineered to first coat themselves with iron phosphate, then attach to carbon nanotubes, in order to create a network of highly conductive material.

Lab tests found that batteries with the new cathode material could be charged and discharged at least 100 times without losing any capacitance. Although that is fewer charge cycles than present-day lithium-ion batteries offer, the expectation is they "will be able to go much longer," said team leader, MIT materials scientist Angela Belcher, in a statement.

The prototype is packaged as a typical coin cell battery. However, the technology allows for the assembly of very lightweight, flexible and conformable batteries that can take the shape of their container.