Ask a regular smartphone user how they'd like to see the devices improved, and it's a safe bet that longer battery life would be close to the top of the list. Batteries made with silicon anodes could help boost that, and now a team at the University of California Riverside (UCR) has shown that these batteries can be environmentally friendly too, by being sourced from glass bottles headed for the scrap heap.
Lithium-ion batteries power everything from smartphones to electric vehicles, and conventionally they're made with a lithium cathode and a graphite anode. But as useful as this setup has been over the years, the ceiling on their efficiency has all but been reached, prompting researchers to look to our old friend silicon as an alternative anode.
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While they have the potential to store up to 10 times more energy than graphite, silicon anodes aren't quite as durable, with the expansion and contraction that comes with regular use cracking the material and wearing them down much faster. Past work has found that crushing the silicon first helped to overcome that problem.
With durability addressed, the UCR team's research has now found a new source of silicon for producing batteries: discarded glass bottles. The researchers aren't strangers to using unusual materials as anodes: in the past, they've dabbled in recipes using sand and mushrooms. Now they've shown that silicon dioxide can be wrung out of glass bottles, saving them from the fate of clogging up landfills.
First, the bottles are crushed and ground down into a fine, white powder. Next, the silicon dioxide is reduced down into nanostructured silicon with the help of hot magnesium, and finally, those nanoparticles are coated in carbon, which makes them more stable and improves their energy storage capacity.
When tested in coin cell batteries over 400 cycles, the bottle-based silicon anodes demonstrated a capacity of about 1,420 mAh/g (milliamp hours per gram), a huge improvement over the storage capabilities of graphite anodes, which typically manage about 350 mAh/g.
"We started with a waste product that was headed for the landfill and created batteries that stored more energy, charged faster, and were more stable than commercial coin cell batteries," says Changling Li, lead author on the study. "Hence, we have very promising candidates for next-generation lithium-ion batteries."
The researchers say that the process is viable, thanks to the low-cost chemical reaction and the fact that each glass bottle can create enough nanosilicon to make hundreds of coin cell batteries. The team has filed a patent to commercialize the process and products.
The study was published in the journal Scientific Reports, and the process is outlined in the video below.