Semiconductor production requires extremely pure wafers of silicon, so with such high standards it is not surprising there is some silicon that cannot be used. Instead of disposing of this silicon though, researchers at Rice University have a way to make it into flexible and efficient batteries. The key is the coating used which keeps the normally fragile material from breaking.
Modern lithium ion batteries use graphite to absorb the lithium ions but silicon is known to be as much as 10 times better at absorbing the ions, so it would be ten times better at storing energy. The reason silicon is not used in batteries though is that it swells so much when it absorbs the ions that it can break, which not only deteriorates the performance of the battery, but can actually damage it. The researchers have solved this by creating silicon nanowires from waste silicon wafers and coating them in copper and a flexible electrolyte. This electrolyte made it possible for the nanowires to be harvested from the wafer without breaking them.
When tested, the silicon nanowires were able to produce 150 milliamp hours per gram with little degradation over 50 charge/discharge cycles. The researchers are working to improve those numbers and to eventually test this design in more standard battery configurations. Hopefully they will succeed as their method to produce the nanowires is relatively simple and could easily be scaled up for production.