It can be a frustrating problem in engineering: having in mind a terrific concept, but no readily available way to implement it. The field of nanotechnology is rife with examples, one being production of lithium-air batteries. With a potential for radically increasing the ratio of weight to charge and power over currently available batteries, lithium-air units are increasingly seen as an ideal battery for electric automobiles. However, numerous obstacles must first be surmounted, chief among them making the batteries economically feasible to produce in light of expensive materials costs. One conceived approach has been to manufacture battery cells with a greater surface area, but how could such a thing be done industrially?
Researchers at the Massachusetts Institute of Technology have developed an innovative solution: to produce nanowires - with the diameter of an average blood cell - to serve as battery electrodes, using a thing in nature already perfectly suited to manufacturing components at the microscopic scale. Namely, viruses.
Specifically, a genetically-engineered virus called M13. Publishing their work in the journal Nature Communications, an MIT team led by graduate student Dahyun Oh, with professors Angela Belcher, Yang Shao-Horn and three others, describe how M13 has been altered into serving as a "nanowire factory," taking in dissolved metals in water solution as the raw materials and from them producing wires measuring 80 nanometers across. The wires are composed of manganese oxide, considered a "favored material" for lithium air batteries. And rather than individual strands, the M13-generated nanowires are in a complex structure of cross-linked mesh, providing greater physical strength and support.
One of the surprising advantages of the virus-manufactured nanowires is that as opposed to traditional means, M13's product has a drastically rougher, spikier surface. Koch Institute for Integrative Cancer Research member Angela Blecher describes the manufacture as, "Really similar to how an abalone grows its shell." The property serves to even more drastically increase the surface area of the nanowires as a whole.
What may prove to be especially enticing for commercial manufacturers is that the MIT-developed method requires no significantly special environments or working conditions to produce. Currently processes for fabrication of such batteries require high temperatures and large amounts of hazardous materials. The MIT team's method is done at room temperature, with readily-available water and simple-to-use metal compounds. The virus-employing system also makes far more efficient use of expensive materials. The final step of the process is the addition of palladium, albeit in far smaller quantities than traditional battery manufacturing. The end result: a battery with 2 to 3 times the charge capacity of the best lithium-ion batteries on the market.
However, for electric-powered cars to be fully embraced by mainstream consumers, other challenges remain to be overcome. Chief among those is the durability of the battery across a lifetime of possibly thousands of charges, discharges and recharges; a problem that has stymied scientists for decades. And the MIT team acknowledges that while their work focused on producing the electrode, the electrolyte - the medium conducting the lithium ions throughout the cell - still requires research to find the perfect material for use. Even so, the MIT team's research represents a significant and cross-disciplined step forward in the fields of nanotechnology.