Researchers at Rice University and the Université catholique de Louvain, Belgium, have developed a method to turn discarded silicon into flexible components for rechargeable batteries. One of silicon’s excellent qualities is that it absorbs ten times more lithium than the carbon currently used in lithium-ion [Li-ion] rechargeable batteries.
The problem is that the silicon expands and contracts so much during recharging and discharging cycles that it destroys itself, making it a poor choice for longevity in rechargeable Li-ion batteries.
Silicon nano-wires, a mere 50 to 70 microns long, were previously produced, but were difficult to utilize, because they simply fell apart on removal. Researchers needed to find a way to encase them to facilitate their use.
By using already established processes, including colloidal nanosphere lithography and chemical etching, to grow the nano-wires, then applying a thin layer of copper, and finally infusing the whole array with an ion-transporting electrolyte, researchers were able to create a thin anode. Later application of the cathode layer would allow the whole matrix to be removed from the original silicon, forming a flexible anode/cathode composite.
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 composite from the original silicon wafer, and after combining with a spray-on current-collecting layer, the resulting Li-ion battery delivered 150 milliamp-hours per gram. The encased nano-wires showed little decay after more than 50 charging cycles.
Reddy hopes that the new process will lead to rechargeable-battery improvements, making them flexible, efficient, and inexpensive. These new developments could also lead to a better solution for responsible electronics-waste management, especially since the silicon chips are both valuable and very hard to recycle.