Sand-based Li-ion batteries

Researchers have created sand-based lithium-ion batteries that are said to outperform the current industry performance standard by three times.

The idea came to Zachary Favors, a graduate student at the University of California, Riverside’s Bourns College of Engineering, when he was relaxing on the beach after surfing in San Clemente, California. He picked up some sand, took a close look at it and saw it was made up primarily of quartz, or silicon dioxide. Favors worked with Cengiz and Mihri Ozkan, both engineering professors at UC Riverside.

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, or billionths of a metre, level 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. He then 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 seawater 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.

The Ozkan team also encountered an added positive surprise. The pure nano-silicon formed in a very porous 3D silicon sponge-like consistency. That porosity has proved to be the key to improving the performance of the batteries built with the nano-silicon.

The improved performance could mean increasing the expected life span of silicon-based electric vehicle batteries up to three times or more, which would be significant for consumers, considering replacement batteries cost thousands of dollars. The energy density is more than three times higher than that of traditional graphite-based anodes, which means mobile phones and tablets could last three times longer between charges.

Now, the Ozkan team is trying to produce larger quantities of the nano-silicon beach sand and is planning to move from coin-size batteries to pouch-size batteries that are used in mobile phones.

The research is supported by Temiz Energy Technologies. The UCR Office of Technology Commercialization has filed patents for inventions reported in the research paper.