Power/Performance Bits: Feb. 17

What can snails teach us about creating batteries?

Evgenia Barannikova, a graduate student at University of Maryland, Baltimore County presented the current state of research in using biology to improve the properties of lithium ion batteries at the 59th annual meeting of the Biophysical Society, held Feb. 7-11 in Baltimore, Maryland.

One of the inspirations for her research was the way that organisms such as mollusks use peptides to control the growth of their shells. “They demonstrate remarkable control in order to build intricate nano- and macrostructures from inorganic materials like calcium carbonate”.

Nanostructured electrodes in Li-ion batteries have several advantages over bulk material electrodes, including shorter distances for charge-carrying particles to travel and a high surface area that provides more active sites for electrochemical reactions to occur – all of which translates to batteries that are lighter and longer-lasting.

Barannikova and her colleagues screened more than one billion possible peptides in search of one that would stick strongly to lithium manganese nickel oxide. The researchers isolated a peptide that binds to lithium manganese nickel oxide by combining the library with a sample of the metal oxide and then repeatedly washing away the peptides that didn’t stick to it.

The researchers then combined the newly-discovered peptide with a previously isolated peptide that binds to carbon nanotubes. Carbon nanotubes can serve as conductive nanowires in Li-ion electrodes.

The team is currently testing how well the new cathodes perform. Going forward, Barannikova plans to make an anode with similar techniques and to integrate the two components. “I hope to demonstrate an entire biotemplated battery in my Ph.D. thesis,” she said.

Lithium manganese nickel oxide and carbon nanotubes clumping separately, with no specific interactions. (Source: Evgenia Barannikova/UMBC)

When a multifunctional binding peptide is added to the mixture the peptide binds the dispersed carbon nanotubes to lithium manganese nickel oxide particles. (Source: Evgenia Barannikova/UMBC)

LEDs instead of lasers – or wires

Lasers are ubiquitous, the reigning workhorse for high-speed optical communications. However, they have downsides for communications over short distances – they consume too much power and typically take up too much space. LEDs would be a much more efficient alternative but have been limited by their spontaneous emission rates.

“Spontaneous emission from molecular-sized radiators is slowed by many orders of magnitude because molecules are too small to act as their own antennas,” Eli Yablonovitch, an electrical engineer with Berkeley Lab’s Materials Sciences Division, says. “The key to speeding up these spontaneous emissions is to couple the radiating molecule to a half-wavelength antenna. Even though we’ve had antennas in radio for 120 years, somehow we’ve overlooked antennas in optics.”

Yablonovitch ‘s team used an external antenna made from gold to effectively boost the spontaneous light emission of a nanorod made from Indium Gallium Arsenide Phosphide (InGaAsP) by 115 times. When a 200-fold increase is reached, spontaneous emission rates will exceed those of stimulated emissions.

Coupling a gold antenna to a InGaAsP nanorod, isolated by TiO2 and embedded in epoxy, greatly enhanced the spontaneous light emission of the InGaAsP. (Source: Berkley Labs)

The results of this study are reported in the Proceedings of the National Academy of Sciences in a paper titled “Optical antenna enhanced spontaneous emission.”

“With optical antennas, we believe that spontaneous emission rate enhancements of better than 2,500 times are possible while still maintaining light emission efficiency greater than 50-percent,” Yablonovitch says. “Replacing wires on microchips with antenna -enhanced LEDs would allow for faster interconnectivity and greater computational power.”