|Specific capacity of one of the a-FePO4 viral nanowires in two-gene systems tested between 2.0 and 4.3V. (EC#2 had the strongest binding affinity to SWNTs). Active materials loading was 2.62 mg/cm2. Lee et al. (2009) Click to enlarge.|
MIT researchers have developed a strategy for using genetically engineered multifunctional viruses as scaffolds for the synthesis and assembly of cathode materials for high-power lithium-ion batteries. By manipulating two genes of the M13 virus (a bacteriophage), the viruses were equipped with peptide groups with affinity for single-walled carbon nanotubes (SWNTs) on one end and peptides capable of nucleating amorphous iron phosphate (a-FePO4) fused to the viral major coat protein to create a iron phosphate cathode material.
The power performance of viral a-FePO4 nanowires was comparable to that of conventional crystalline lithium iron phosphate (c-LiFePO4), and the team reported excellent capacity retention upon cycling at 1C for at least 50 cycles. The synthesis takes place at and below room temperature, requires no harmful organic solvents, and the materials that go into the battery are non-toxic. A paper on the work was published online in the journal Science on 2 April.
The team was led by Angela Belcher, the Germeshausen Professor of Materials Science and Engineering and Biological Engineering and included MIT Professor Gerbrand Ceder of materials science and Associate Professor Michael Strano of chemical engineering. Three years ago, an MIT team led by Belcher showed that the M13 virus could be used for battery device fabrication with improved performance by synthesizing electrochemically active anode nanowires and organizing the virus on a polymer surface.
In the latest work, the team focused on building a cathode. For this, they required the virus to be multifunctional to overcome some of the complexity of building a cathode—e.g. although the cathodes must be highly conducting to be a fast electrode,most candidate materials for cathodes are highly insulating.
Because the modified 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 via the biological scaffold. Electrons can travel along the carbon nanotube networks throughout the electrodes to the iron phosphate and transferring energy in a very short time.
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.
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.
Now that the researchers have demonstrated 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, said Belcher. Once that next generation is ready, the technology could go into commercial production, she said.
Lead authors of the Science paper are Yun Jung Lee and Hyunjung Yi, graduate students in materials science and engineering. Other authors are Woo-Jae Kim, postdoctoral fellow in chemical engineering; Kisuk Kang, recent MIT PhD recipient in materials science and engineering; and Dong Soo Yun, research engineer in materials science and engineering.
The research was funded by the Army Research Office Institute of the Institute of Collaborative Technologies, and the National Science Foundation through the Materials Research Science and Engineering Centers program.
Yun Jung Lee, Hyunjung Yi, Woo-Jae Kim, Kisuk Kang, Dong Soo Yun, Michael S. Strano, Gerbrand Ceder, and Angela M. Belcher (2009) Fabricating Genetically Engineered High-Power Lithium Ion Batteries Using Multiple Virus Genes. Science doi: 10.1126/science.1171541