Sand is the holy grail of Li-ion anodes

The electronics industry has its pillars built upon silicon, which is said to be the second most common element in the earth's crust, after oxygen. And silicon is present in sand, a key material used by researchers at the University of California, Riverside's Bourns College of Engineering in creating a Li-ion battery that outperforms the current industry standard by three times.

The idea using sand came half a year ago to Zachary Favors, a graduate student working with Cengiz and Mihri Ozkan, both engineering professors at UC Riverside: a warm day spent sprawled on the beach after hours of surfing. Favors closely examined some sand and found that it was composed primarily of quartz, or silicon dioxide.

"This is the holy grail – a low cost, non-toxic, environmentally friendly way to produce high performance lithium ion battery anodes," said Favors.

His research is centred on building better Li-ion batteries, primarily for personal electronics and electric vehicles. He is focused on the anode, or negative side of the battery. Graphite is the current standard material for the anode, but as electronics have become more powerful graphite's ability to be improved has been virtually tapped out.

Researchers are now focused on using silicon at the nanoscale level, or billionths of a metre, as a replacement for graphite. The problem with nanoscale silicon is that it degrades quickly and is hard to produce in large quantities.

Favors set out to solve both these problems. He researched sand to find a spot in the United States where it is found with a high percentage of quartz. That took him to the Cedar Creek Reservoir, east of Dallas, where he grew up.

Sand in hand, he came back to the lab at UC Riverside and milled it down to the nanometre scale, followed by a series of purification steps changing its colour from brown to bright white, similar in colour and texture to powdered sugar.

After that, he ground salt and magnesium, both very common elements found dissolved in sea water into the purified quartz. The resulting powder was then heated. With the salt acting as a heat absorber, the magnesium worked to remove the oxygen from the quartz, resulting in pure silicon.

Figure 1: From left, (b) unpurified sand, (c) purified sand, and (d) vials of unpurified sand, purified sand, and nano silicon. Source: UCR

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