GENETICALLY engineered viruses that assemble into electrodes have been used to make complete miniature rechargeable batteries for the first time. The new lithium ion batteries are as powerful as existing devices but smaller and cleaner to make, claim the team behind the work. The technology could improve the performance of hybrid electric cars and electronic gadgets.
Lithium ion batteries exploit the reactivity of lithium to produce a current. Inside the battery, lithium ions move from the anode to the cathode, forcing electrons in the opposite direction around an external circuit. This process is reversed when the battery is recharged.
Making these batteries takes a tough manufacturing process because of the highly reactive components, aggressive solvents and high temperatures used in construction, as well as the dangers of handling lithium.
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Viruses could make this process much safer and cleaner, says at the Massachusetts Institute of Technology. Her team converted a harmless virus called M13 into a cathode by inserting a gene that causes the virus to produce proteins that bond with iron and phosphate ions in a surrounding solution. As a result, the long, tubular virus particles become sheathed in an 鈥渁rmour plating鈥� of iron phosphate, turning them into nanowires.
The resultant batteries were not as good as commercial models, however 鈥� the cathodes turned out to be good at conducting lithium ions but not electrons.
To solve this, the team inserted a second gene that creates a protein at the tip of the virus that bonds to a carbon nanotube. The nanotube increases the electron conductivity of the combined structure (see diagram). 鈥淲e were basically adding a highway that allows the electrons to move in and out rapidly,鈥� says Belcher.
The resulting battery turned out to be as good as the best commercially available that use crystalline lithium iron phosphate materials (Science, ). And since the team had previously used the same viral technique to produce anodes (快猫短视频 online, 6 April 2006), it has now been able to make a full virus-based 3-volt lithium ion battery.
Compared to conventional lithium ion batteries, the biologically grown battery is environmentally friendly because much of the materials can now be made at room temperature or on ice and without harsh solvents. 鈥淚t鈥檚 a pretty simple process that doesn鈥檛 require fancy equipment,鈥� says Belcher.
鈥淚t鈥檚 environmentally friendly because much of its materials can be made at room temperature鈥�
It has potential to be even better, though. This production system could boost battery performance because it uses nanostructured materials that can store and release more power than conventional materials, and also do it faster. Already Belcher鈥檚 prototype battery is as powerful as existing technologies, an ability she has shown off by using one to power an LED. Her team is now investigating materials that work at higher voltages and with higher energy-storage capacities.
Joachim Maier, at the Max Planck Institute for Solid State Research in Stuttgart, Germany, reckons using biology is a useful approach. 鈥淣ot too many people look into biology in this context, so from that point of view it is very interesting,鈥� he says.
