In recent years, lithium-air batteries that promise improved power density per pound over lithium-ion batteries have been the subject of much research in the quest to give electronic vehicles greater range. By enlisting the help of a genetically-modified virus, researchers at MIT have found a way to improve the performance and durability of lithium-air batteries, which offer the potential of two to three times the energy density of current lithium-ion batteries.
The main reason lithium-air batteries boast higher energy density than lithium-ion batteries is because, in place of the heavy conventional compounds used in lithium-ion batteries, they use oxygen from the air to react with a lithium anode through a carbon-based air cathode. Nanowires used as one of the electrodes for these batteries are typically created through a high-energy chemical process, which produces electrodes with a flat surface area.
By using a genetically modified version of the M13 virus, the MIT team was able to increase the surface area of a nanowire array, which is about 80 nm across. The virus has the ability to “capture molecules of metals from water and bind them into structural shapes,” says Angela Belcher, the W.M. Keck Professor of Energy and a member of MIT’s Koch Institute for Integrative Cancer Research. "Similar to how an abalone grows its shell.”
The viruses built wires of manganese oxide, a material often used for the cathode of lithium-air batteries, that had a rough, spiked surface. Having spikes, rather than a flatter surface as results when wires are “grown” through conventional chemical methods, creates more surface area for the chemical reaction to occur. This process also creates a cross-linked 3D structure, rather than isolated wires, making for a more stable electrode. Adding to its advantages, the viral process is water-based and done at room temperature.
This doesn’t mean that our battery-making facilities will become industrial virus churns, as Belcher expects the manufacturing process to evolve, as it has with other materials developed in her lab in the past. “The chemistry was initially developed using biological methods, but then alternative means that were more easily scalable for industrial-scale production were substituted in the actual manufacturing.”
The researchers only produced a cathode using the viral process and the produced material was tested through 50 cycles of charging and discharging, which is a drop in the bucket compared to the thousands of cycles electric vehicle batteries would endure. According to the team, more research is needed, specifically in the area of the electrolyte of the battery, to make lithium-air batteries commercially viable.
A paper about the research was published in the journal Nature Communications.
The video below gives an overview of the process the virus uses to create a spiky nanowire.