Rice University Team Builds Lithium Ion Battery into a Single Nanowire
Rice University scientists have packed an entire lithium ion energy storage device into a single nanowire. Led by Prof. Pulickel Ajayan, professor of mechanical engineering and materials science, the team believes their work could prove valuable as a rechargeable power source for new generations of nanoelectronics.
Rice researchers tested two versions of their battery/supercapacitor hybrid.
- The first version is a sandwich with nickel/tin anode, polyethylene oxide (PEO) electrolyte and polyaniline cathode layers. It was built to prove that lithium ions would move efficiently through the anode to the electrolyte and then to the supercapacitor-like cathode. The cathode stores the ions in bulk and gives the device the ability to charge and discharge quickly).
- The second version packs the same capabilities into a single nanowire. Researchers built centimeter-scale arrays containing thousands of nanowire devices (approx 150 nms wide).
"The idea here is to fabricate nanowire energy storage devices with ultrathin separation between the electrodes," said Arava Leela Mohana Reddy, a research scientist at Rice and co-author of the paper. "This affects the electrochemical behavior of the device. Our devices could be a very useful tool to probe nanoscale phenomenon."
Ajayan's team first reported the creation of three-dimensional nanobatteries last December, when they encased vertical arrays of nickel-tin nanowires in PMMA (a polymer also known as Plexiglas).
The team grew the nanowires via electrodeposition in an anodized alumina template atop a copper substrate. They widened the template's pores with a simple chemical etching technique that created a gap between the wires and the alumina, and then drop-coated PMMA to encase the wires in a smooth, consistent sheath. A chemical wash removed the template and left a forest of electrolyte-encased nanowires.
For that earlier battery, the encased nickel-tin was the anode, but the cathode had to be attached on the outside.
The team’s new process tucks the cathode inside the nanowires, according to Ajayan. In this feat of nanoengineering, the researchers used PEO as the gel-like electrolyte that stores lithium ions and also serves as an electrical insulator between nanowires in an array.
After much trial and error, the Rice researchers settled on an easily synthesized polymer known as polyaniline (PANI) as their cathode. Drop-coating the widened alumina pores with PEO coats the insides, encases the anodes and leaves tubes at the top into which PANI cathodes could also be drop-coated. An aluminum current collector placed on top of the array completes the circuit.
"There's a lot to be done to optimize the devices in terms of performance," said the paper's lead author, Sanketh Gowda, a chemical engineering graduate student at Rice. "Optimization of the polymer separator and its thickness and an exploration of different electrode systems could lead to improvements." Rice graduate student Xiaobo Zhan is a co-author of the paper.
The Hartley Family Foundation, Rice University, National Institutes of Health, Army Research Office and Multidisciplinary University Research Initiative supported the research. The work appears in the July edition of the American Chemical Society journal Nano Letters.