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Waste silicon gets new life in lithium-ion batteriesThe silicon/copper/polymer composite can be rolled from its silicon substrate and leave a mask in place to begin anew the process of making another anode for a lithium-ion battery. Credit: Alexandru Vlad/Rice University
Researchers at Rice University and the Université catholique de Louvain, Belgium, have developed a way to make flexible components for rechargeable lithium-ion (LI) batteries from discarded silicon.
The Rice lab of materials scientist Pulickel Ajayan created forests of nanowires from high-value but hard-to-recycle silicon. Silicon absorbs 10 times more lithium than the carbon commonly used in LI batteries, but because it expands and contracts as it charges and discharges, it breaks down quickly.
The Ajayan lab reports this week in the journal Proceedings of the National Academy of Science on its technique to make carefully arrayed nanowires encased in electrically conducting copper and ion-conducting polymer electrolyte into an anode. The material gives nanowires the space to grow and shrink as needed, which prolongs their usefulness. The electrolyte also serves as an efficient spacer between the anode and cathode.
Transforming waste into batteries should be a scalable process, said Ajayan, Rice's M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry. The researchers hope their devices are a step toward a new generation of flexible, efficient, inexpensive batteries that can conform to any shape.
Co-lead authors Arava Leela Mohana Reddy, a Rice research scientist, and Alexandru Vlad, a former research associate at Rice and now a postdoctoral researcher at the Université catholique de Louvain, were able to pull multiple layers of the anode/electrolyte composite from a single discarded wafer. Samples of the material made at Rice look like strips of white tape or bandages.
Rice University research scientist Arava Leela Mohana Reddy holds strips of anode material and a piece of waste silicon (at left). Researchers at Rice and in Belgium found a way to recycle silicon into flexible anodes for lithium-ion batteries. Credit: Jeff Fitlow, Rice University
They used an established process, colloidal nanosphere lithography, to make a silicon corrosion mask by spreading polystyrene beads suspended in liquid onto a silicon wafer. The beads on the wafer self-assembled into a hexagonal grid and stayed put when shrunken chemically. A thin layer of gold was sprayed on and the polystyrene removed, which left a fine gold mask with evenly spaced holes on top of the wafer. "We could do this on wafers the size of a pizza in no time," Vlad said.
The mask was used in metal-assisted chemical etching, in which the silicon dissolved where it touched the metal. Over time in a chemical bath, the metal catalyst would sink into the silicon and leave millions of evenly spaced nanowires, 50 to 70 microns long, poking through the holes.
