Essentially, the concept behind the work is to modify the genes of the M13 virus—the inherent structural characteristics of which make it an excellent template for the synthesis of various functional nanowires—to display modified proteins with affinities for specific materials.

In the current work, the team engineered two clones—one for specificity and one for versatility—to synthesize noble metal nanowires with diameters below 50 nm with control over particle sizes, morphologies and compositions.

Under testing, they found that the first discharge capacity of all the alloys were all similar with values 900-965 mAh/g, but because of the high first cycle irreversible capacity, the second discharge capacities dropped to 440-534 mAh/g depending on the alloy composition. By comparison, for most Ag and Au thin film anodes, the discharge capacity has been reported as 500-600 mAh/g at the first cycle and decreased to 100-200 mAh/g in 10 cycles.

Biological systems offer capabilities for environmentally benign materials synthesis. The two M13 viruses, genetically engineered for specificity (p8#9 virus) and versatility (E4/ E3 virus) served as a template for the synthesis of noble metal nanowires with diameters below 50 nm. The inherent structural characteristic of the M13 virus enabled the synthesis of high aspect ratio nanowires. With the synergetic combination of biological building blocks and synthetic chemistry, this facile and high-yield synthesis conferred controls over particle size, morphology, and compositions.

The biologically derived noble metal and alloy nanowires with diameter below 50 nm showed electrochemical activities toward lithium comparable to thin film electrodes. Improvement in capacity retention was achieved by tailoring particle size, alloy formation, and surface stabilization.

Because Au and Ag react poorly with lithium at the micrometer scale, fundamental study on their electrochemical behavior has been limited so far. Although these materials are not as cost-effective as existing anode materials, these nanowires serve as a model system in identifying important parameters that can induce stable electrochemical transformation at the nanoscale.

This study elucidated the importance of surface characteristics and reaction/phase homogeneity in maintaining structural stability and electrochemical performances at the nanoscale. The principles found in this model system can be applied to improve structural stability of other technologically important alloy material systems. With advantages of facile and environmentally benign synthesis, M13 biological platform proved itself as a useful toolkit for the study on the basic electrochemical property of materials.

—Lee et al.

Resources

• Yun Jung Lee, Youjin Lee, Dahyun Oh, Tiffany Chen, Gerbrand Ceder and Angela M. Belcher (2010) Biologically Activated Noble Metal Alloys at the Nanoscale: For Lithium Ion Battery Anodes. Nano Lett., Article ASAP doi: 10.1021/nl1005993