Conventional lithium-ion batteries rely on anodes made of graphite, but it is widely believed that the performance of this material has reached its zenith, prompting researchers to look at possible replacements. Much of the focus has been on nanoscale silicon, but it remains difficult to produce in large quantities and usually degrades quickly. Researchers at the University of California, Riverside have overcome these problems by developing a lithium-ion battery anode using sand.
When Zachary Favors, a graduate student at UC Riverside working on developing better lithium-ion batteries, noticed that the beach sand he was relaxing on after surfing in San Clemente, California was primarily made up of quartz, or silicon dioxide, it prompted him to delve a little deeper. Researching where in the US sand could be found with a high percentage of quartz, he ended up at the Cedar Creek Reservoir in Texas.
He collected some of the sand and took it back to a lab at the Bourns College of Engineering at UC Riverside where he worked with engineering professors Cengiz and Mihri Ozkan. Favors started milling the sand down to the nanometer scale before putting it through a series of purification steps that gave it a similar color and texture to powdered sugar.
He then ground salt and magnesium into the purified quartz and heated the resulting powder. In this very simple process, the salt acted as a heat absorber while the magnesium removed oxygen from the quartz, resulting in pure silicon. More than that, the pure nano-silicon formed in a very porous, 3D silicon sponge-like consistency. Porosity is one of the keys to improving the performance of battery anodes as it provides a large surface area and allows lithium ions to travel through them more quickly.
The team has developed a coin-sized lithium-ion battery using the new anode that they claim significantly outperforms conventional lithium-ion batteries. They say the improved performance of the nano-silicon electrode could be expected to equate to a threefold increase in battery life for devices such as mobile phones, which would only need to be recharged every three days rather than every day, and electric vehicle batteries that last three times longer, cutting down on expensive replacement costs.
The researchers are now looking to produce the nano-silicon in larger quantities and move from coin-size batteries to pouch-size batteries like those used in mobile phones.
Patents have been filed for the technology, which is detailed in the journal Scientific Reports.