Viruses electrify battery research

A new approach to making battery electrodes with the help of genetically engineered viruses could reduce costs and improve environmental sustainability.

Figure 1 | Biomimetic electrodes for lithium-ion batteries. Belcher and co-workers have shown that genetically modified M13 viruses can be used to make negative electrodes based on Co3O4 nanowires and gold nanoparticles3 (bottom), and positive electrodes based on a-FePO4 nanowires and carbon nanotubes (CNT, top)2. This particular pair of electrodes could not be used together because a Co3O4 negative electrode requires a lithium-based positive electrode.

Figure 1 | Biomimetic electrodes for lithium-ion batteries. Belcher and co-workers have shown that genetically modified M13 viruses can be used to make negative electrodes based on Co3O4 nanowires and gold nanoparticles3 (bottom), and positive electrodes based on a-FePO4 nanowires and carbon nanotubes (CNT, top)2. This particular pair of electrodes could not be used together because a Co3O4 negative electrode requires a lithium-based positive electrode.

Jean-Marie Tarascon

Over the past two decades, the performance of rechargeable lithium-ion batteries has improved greatly1, and these batteries now offer both high energy density (~200 W h kg1) and high specific power (~4.5 kW kg1). This performance makes them attractive for use in applications such as hybrid and electric cars, and solar and wind energy storage. Challenges to be overcome include lowering costs, improving safety and reducing environmental impact.

Lithium-ion batteries rely on the extraction of positive lithium ions from one electrode and their insertion into the other. Electrons flow at the same time in the external circuit. Research has focused on new electrode materials, and several cheap and abundant examples have been recently identified. These include iron-based phosphates and silicates, made from elements that are major constituents of the Earths crust and are therefore practically unlimited in quantity.

There is, however, one important drawback to these otherwise attractive materials: their extremely low ionic and electronic conductivity. This can be partially addressed by using nanoscale materials to shorten the distances that the electrons and the lithium ions have to travel. Although the advantages of nanostructured electrodes are well understood, their rational design remains a key challenge for the chemistry and materials communities. In particular, a critical question for battery researchers today is whether nanostructured electrodes can be made by eco-efficient processes with a small carbon footprint.

Now in Science, Angela Belcher and colleagues at Massachusetts Institute of Technology (MIT) and the Korea Advanced Institute of Science and Technology (KAIST) report an elegant way of addressing some of these concerns2. Building on previous work in which they showed how a virus called M13 can be genetically engineered (Fig. 1, bottom) to provide a template for the growth of negative electrodes3, Belcher and colleagues now apply the same biological principles in a new direction: the growth of a positive electrode based on amorphous iron phosphate (a-FePO4). They find that engineering a single virus gene to nucleate iron phosphate results in electrodes that have acceptable capacity retention upon cycling but limited high-power performance. The common response of the battery community to such poor kinetics is to add an electronic conductor, generally a form of carbon, to the mix. Two of the most popular approaches are carbon nanopainting, which gives a thin coating of carbon to the electrodes, and the mechanical addition of carbon nanotubes. Although nanopainting produces a better interface than carbon nanotubes, it also requires high-temperature processing under a reducing environment, preventing its use for oxidizing materials such as ferric oxides .

It is here that the coup de force of the paper is found. Belcher and colleagues improve the performance of their iron phosphate electrodes with a new way of incorporating carbon nanotubes (Fig. 1, top). They

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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