Left. Lithium manganese nickel oxide and carbon nanotubes clumping separately, with no specific interactions. Right. When a multifunctional binding peptide is added to the mixture, the peptide binds the dispersed carbon nanotubes to lithium manganese nickel oxide particles. Credit: Evgenia Barannikova/UMBC. Click to enlarge.

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. However, nanoscale materials can be hard to control and hold in place.

To take on the challenge of manufacturing on the nanoscale the UMBC team turned to peptides. Themselves made up from strings of amino acids, peptides are naturally occurring and bind to many different types of organic and inorganic materials, depending on their sequence of the amino acids. They play many roles in the human body, from signaling in the brain to regulating blood sugar; some drugs, such as insulin, are made up of peptides.

One of the inspirations for the research, said Evgenia Barannikova, a graduate student at UMBC, 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.

Barannikova and her colleagues used a procedure called “Phage Display” to screen more than one billion possible peptides in search of one that would stick strongly to lithium manganese nickel oxide. The “peptide library” through which the researchers searched is commercially produced by a laboratory supply company, and contains a vast number of randomly combined amino acid sequences incorporated into a protein made by a virus called the M13 bacteriophage.

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 resulting peptide could then form a bridge, binding to both the lithium manganese nickel oxide nanoparticles and the carbon nanotubes and keeping them close to each other so that they can maintain a connection through multiple charging cycles. By helping to maintain a highly organized architecture at the nanoscale, the researchers expect that their peptides will improve the power and cycling stability of future Li-ion batteries, allowing them to be smaller and maintain longer lifetimes.

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.