Normally, when a scientist spends a good portion of their life in a lab, trying to engineer a technological breakthrough, the last they want is to see that work destroyed. But as researchers at Rice University recently discovered, crushing their previous work can sometimes be the only way to make progress.
A Rice team has been trying to refine silicon-based lithium-ion battery technology. According to the researchers, silicon can hold 10 times more lithium ions than the graphite commonly used in anodes today. Sounds great, right? But there’s a problem: silicon expands when completely lithiated, sometimes to more than three times its original size. Over time, this repeated swelling and shrinking causes silicon to quickly break down.
In previous research, Rice University scientists created nanostructured silicon with a high surface-to-volume ratio, which allows the silicon to accommodate a larger volume expansion. In current research, Rice engineer Sibani Lisa Biswal and research scientist Madhuri Thakur tried the opposite approach; they etched pores into silicon wafers to give the material room to expand. By earlier this year, successfully made promising sponge-like silicon films. But the original problems still lingered: they weren’t easy to handle and would be nearly impossible to scale. Then, Biswal and Thakur decided to take a page from the Incredible Hulk, and started smashing.
By crushing the sponges into porous grains, the team realized that the material gained far more surface area to soak up lithium ions, drastically increasing surface area, and thus capacity, without increasing cost. “As a powder, they can be used in large-scale roll-to-roll processing by industry,” Thakur said. “The material is very simple to synthesize, cost-effective and gives high energy capacity over a large number of cycles.” They say the next step will be to test this porous silicon powder as an anode in a full battery.