A former Tesla battery scientist and 3 other experts lay out the challenges Elon Musk will face with silicon batteries, a technology that's stymied researchers for decades

  • Elon Musk said Tesla is working on battery technology that would halve the cost per kilowatt hour, making EVs cost-competitive with gas-guzzling cars. 
  • During Tesla's outdoor "battery day" Tuesday, Musk revealed the firm would make electrodes for its batteries using metallurgical-grade silicon, a lower-quality and cheaper version of the material.
  • Silicon stores a lot of energy, but it comes with significant challenges that startups like Sila Nanotechnologies have spent years ironing out.
  • Tesla claims it has a way to overcome the element's challenges, but experts who spoke to Business Insider remain skeptical.
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Elon Musk just revealed the new technologies that he said will halve the cost of Tesla battery packs, potentially making the firm's future cars more affordable than their gas-guzzling rivals. Steep price tags have long been a major roadblock to widespread EV adoption. 

During an outdoor investor presentation on Tuesday, Musk said his firm overhauled its battery design including the chemistry of the anode, part of the cell that stores charge.

Tesla's new cells, to be manufactured in-house, will use metallurgical-grade silicon in the battery's anode. Metallurgical silicon is cheaper and less-refined than 100% pure silicon. 

The new approach could increase the range of Tesla cars by a staggering 20%, Drew Baglino, SVP of powertrain and energy engineering, said during the event. 

"What we're proposing is a step-change in capability and a step-change in cost," Baglino said.

Musk said it will take "about three years" to realize the full cost and range benefits he and Baglino laid out on Tuesday. 

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While silicon can increase a battery's energy density, the element is notoriously difficult to work with. As it absorbs charge, silicon expands dramatically, which can degrade the cell. And this problem has stymied the battery industry for years.

Surprising some onlookers, Baglino said Tesla has found a solution to this challenge.

The firm's approach differs from its rivals — some of which have been working on silicon anodes for years — and would cost a lot less, enabling cheap electric cars. 

Four battery experts Business Insider spoke to, however, remain skeptical, and say Tesla is likely to face similar challenges that other companies including Daimler-backed Sila Nanotechnologies have been trying to address for nearly a decade, only recently developing commercial products.

"It almost seems too good to be true," analysts at the research firm Wood Mackenzie said in a note Wednesday. "The handful of novel technologies presented will need time to be proven and commercialized."

Tesla did not respond to a request for comment. 

Tesla's Model YTesla

The pros and pitfalls of silicon

Silicon anodes have long been a holy grail in the race to make a better battery.

The material, found in solar panels and semiconductors, is cheap, abundant, and about five times more energy-dense than graphite, which dominates anode chemistry in lithium-ion cells today, according to Matthew Keyser, a battery expert at the National Renewable Energy Laboratory.

The element, however, has a major drawback: As it absorbs ions, silicon expands in size by a factor of three, and then it contracts as it discharges them, Keyser said. When that happens, the surface of the silicon cracks, triggering a reaction between the silicon and the electrolyte that eats up ions of lithium, degrading the cell over time. 

Tesla joins the race to make better silicon cells

Eyeing massive EV range and cost improvements, companies have spent years trying to build silicon anodes with limited degradation. 

Unicorn startup Sila Nanotechnologies and Advano, a newer firm backed by iPod engineer Tony Fadell, for example, encase particles of silicon inside a semiporous spongelike structure. As silicon absorbs the ions, it expands inside the holes while the volume of the sponge stays about the same. That limits the surface cracking.  

Sila Nanotechnologies already has a commercial product it says can increase energy density in battery cells by about 20%. 

Read more: A startup backed by iPod designer Tony Fadell just emerged from stealth with $18.5 million to bring breakthrough batteries to market in massive quantities

Other companies including Amprius are developing what Keyser calls 3D architectures. Essentially, they coat a conductive surface, such as copper, with microscopic columns of graphite, around which they place particles of silicon. As the silicon "expands and contracts, it can expand in the space between the columns," Keyser said. 

Tesla, on the other hand, has proposed a different approach — and it doesn't involve building any kind of architecture to house the silicon. 

Tesla/Youtube

During Tuesday's event, Tesla laid out how it will make the new batteries. The company said it will start with particles of metallurgic silicon.

It will then coat those particles with a flexible polymer, likely made of carbon, that expands along with the silicon as it absorbs electrons, potentially reducing the reaction and cracking that follows.

The silicon will then be enmeshed inside the cell with some kind of elastic binding agent, Baglino said. He didn't say what percent of the new anodes would be comprised of silicon.

Today, Tesla's anodes, which are manufactured by Panasonic, are about 5% silicon already, according to Chloe Holzinger, a senior battery analyst at the data firm IHS Markit. 

Founders of the unicorn battery startup Sila Nanotechnologies. From left; Gleb Yushin, Gene Berdichevsky, and Alex Jacobs.Sila Nanotechnologies

Experts remain skeptical

Tesla provided limited details on its approach, and it has drawn skepticism from battery experts. 

For one, metallurgical-grade silicon is about 98% pure silicon, which means it has impurities. (Competitors like Sila Nanotechnologies use a much purer form of the element.) 

"He wants to use a lower-grade silicon and get a result that's better than what people get with a higher-grade silicon," said Yury Gogotsi, a battery researcher at Drexel University. "That's going to be a challenge. Impurities are known to degrade the electrolyte in batteries." 

It's likely that Tesla will further refine the metallurgical silicon to reach a higher level of purity, however, Keyser said. That would likely increase the battery's cost. 

Tesla may also run into the time-old problem of cracking, according to Keyser and Gene Berdichevsky, the CEO of Sila Nanotechnologies and employee number 7 at Tesla. 

Tesla's CEO, Elon MuskOdd Andersen/AFP via Getty Images

"That approach has been around for a decade," Berdichevsky said. "It's been used for a while and it just doesn't work. You can't protect the silicon particles with the polymer well enough. As the silicon expands and contracts, it's going to damage whatever polymer coating you have on it." 

Berdichevsky doubts Tesla will be able to boost the range of its cars by 20% through this technology alone. 

Depending on the details of Tesla's tech, Gogotsi says the issue that Berdichevsky describes might not be a big problem. Cracking will occur on the outside of the polymer, he said, but that might not rapidly degrade the cell. 

Regardless, losing charge over time may soon be an insignificant problem for Tesla as it builds out its recycling capabilities, Holzinger said, because customers could simply get a replacement battery as soon as the one in their car starts to degrade.

"If Tesla were to build out a recycling program, it wouldn't necessarily matter too much if cycle life took a bit of a hit," she said. 

While a lot of details remain unknown, what is clear is that Tesla is prioritizing cost — the main impediment to growing market share in the transportation sector.

The drawbacks to working with metallurgical-grade silicon may be outweighed by cost-reductions, which Tesla desperately needs. Elon Musk said Tuesday it plans on selling a $25,000 electric car within the next three years. 

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