In the future, lithium-ion batteries may be produced in a test tube. Engineers at Massachusetts Institute of Technology (MIT) have manipulated 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 state-of-the-art rechargeable devices being considered for automotive applications, claims Angela Belcher, an MIT professor of materials science and engineering who specializes in biological engineering. “The new batteries could be manufactured with a cheap and environmentally benign process,” she adds.

In a traditional battery, lithium ions flow between a negatively charged anode—usually graphite—and a positively charged cathode—usually cobalt oxide or lithium iron phosphate. Three years ago, Belcher and her colleagues engineered viruses that could build an anode by coating themselves with cobalt oxide and gold and self-assembling to form a nanowire. The synthesis takes place at and below room temperature and requires no harmful organic solvents; the materials that go into the battery are nontoxic.

Recently, the MIT engineers built a highly powerful cathode to pair up with the anode. “Cathodes are more difficult to build than anodes because they must be highly conducting to be a fast electrode,” notes Belcher. “However, most candidate materials for cathodes are highly insulating and nonconductive.”

To solve that challenge, Belcher reached out to other MIT professors with expertise in materials science and chemical engineering. The team 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 recognize and bind specifically to certain materials (carbon nanotubes in this case), each iron phosphate nanowire can be electrically ‘wired’ to conducting carbon nanotube networks,” explains Belcher. “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 are a common bacteriophage, which infect bacteria but are harmless to humans.”

Belcher and her colleagues discovered 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,” notes Belcher.

“The prototype is packaged as a typical coin cell battery, but the technology allows for the assembly of very lightweight, flexible and conformable batteries that can take the shape of their container,” claims Belcher. “We intend to pursue even better batteries using materials with higher voltage and capacitance, such as manganese phosphate and nickel phosphate. Once that next generation is ready, the technology could go into commercial production.”