Salt and Sand

| September 13, 2017

Two USC Viterbi Professors are doing uncommon things with very common materials.

Aiichiro Nakano, left, and Chongwu Zhou with an abundance of salt and sand at Santa Monica beach, just miles from USC.

Salt and sand: Two common, cheap, and downright boring materials found in abundance at any Southern California beach. They aren’t as flashy as gold, as intimidating as uranium, or as life-sustaining as that periodic prima donna oxygen. But cheap abundance is exactly what makes them so groundbreaking in the work of two USC Viterbi professors.

Salt – Sodium (Na)

Chongwu Zhou, USC Viterbi professor of electrical engineering, uses sodium to make cell phone batteries cheaper and cleaner.  Current cell phone technology uses graphite to store lithium, which acts as the power source. Researchers have long known that sodium could be a better option than lithium but, unfortunately, sodium ions are too large to be stored in graphite.

Zhou, along with doctoral student Yihang Liu, succeeded in building a new, sodium-friendly storage unit out of red phosphorous placed on graphene sheets. Their groundbreaking, wave-like design was the key innovation that brought practical sodium ion batteries into reality. Their work was recently published in ACS Nano.

Sodium is better in a lot of ways. It is much cleaner than lithium, which contributes heavily to climate change and pollution. Because of its abundance, sodium is also cheaper than lithium, which must be mined. Also, you can’t line the top of your margarita glass with lithium.

“Imagine being able to walk right up to the ocean just a few miles from here, and get all the salt you need to manufacture all the world’s cell phone batteries,” said Liu.

And, in what millennials are calling “the greatest scientific achievement known to man,” Zhou’s sodium ion battery can be charged to 50 percent capacity in just two minutes!

The next step for Zhou and his team is to improve the performance and life of their battery so they can bring it to market. But don’t get all salty just because this new battery isn’t ready yet – commercial sodium ion batteries are on the way in the foreseeable future.

Sand – Silica (SiO2)

Aiichiro Nakano, USC Viterbi professor of computer science, loves pressure. Along with professor Fuyuki Shimojo of Kumamoto University, USC Viterbi professors Rajiv Kalia and Priya Vashishta, and others in Japan and Germany, they are taking silica (oxidized silicon), which is found in abundance in sand, and putting it under extreme pressure to create a new ceramic. Their work was recently published in Science Advances Journal and is funded by the Department of Energy.

This material is tough and hard. Meaning it’s strong enough to withstand impact, but not brittle. Add to this the fact that it’s made cheaply out of pressurized silicon and you have a unique material indeed.

But that’s only the start of what makes Nakano’s material special. This ceramic is actually made up of tiny grains called nano-polycrystalline stishovites (NPS). “When the material does eventually crack or tear, these little grains pop like popcorn, effectively sealing and repairing the break,” said Nakano.

The end-product, which is stronger, cheaper, more heat-resistant and lighter than most metals could have countless ramifications.  Theoretically, a tank made entirely out of this ceramic would weigh a fraction of what they do now. Shipping costs could plummet, while vehicle fuel efficiency could skyrocket.

Nakano and his team suspected that their new extreme-pressure method could be applied to other Earth-abundant materials. Their suspicions were confirmed when they successfully applied it to the mineral Magnesium Silicate (MgSiO3), meaning that all kinds of materials with yet-to-be imagined properties could be made.

Thanks to these two USC Viterbi professors, sodium and silica have regained their rightful place at the top of periodic pecking order.  In a coincidental twist of fate, Nakano was a committee member on Liu’s Ph.D. qualifying exam, where he presented his research into red phosphorous. The two shared ideas and hope to combine Nakano’s expertise in computational simulation of materials with Zhou’s work on nano-materials for a future project. With their powers combined, who knows which element will be the next to be reimagined?