Two of the most sacred numbers in the electric-vehicle industry are 300 miles and $100. The first is generally considered to be the distance electric cars need to travel on a single charge for Americans to take them seriously. The second is the cost, per kilowatt-hour, to which batteries need to drop before EVs can compete with gas-powered cars on sticker price.
Sakti3, a Michigan startup that auto-industry insiders have been whispering about for years, says it might soon hit those two sacred targets. The company has long been in semi-stealth mode, talking to the press but offering few particulars about its technology. Now, Ann Marie Sastry, co-founder and CEO of the company, tells me that the company’s prototype solid-state lithium battery cells have reached a record energy density of 1,143 Watt-hours per liter— more than double the energy density of today’s best lithium-ion batteries.
Sakti3’s technology is solid-state battery produced with the same thin-film deposition process used to make flat panel displays and photovoltaic solar cells. The cell contains no liquid electrolyte; an “interlayer” acts as both the separator, which keeps the positive and negative electrodes from coming into contact, and the electrolyte, allowing desirable ion transfers to take place. Sastry says Sakti3 will commercialize its technology in a couple of years, and the first application will be consumer electronics. If all goes according to plan, electric-vehicle batteries will follow. And if Sakti3 delivers what it says it has, it could be the kind of battery to give us the 300-mile, $25,000 electric car.
Before everyone starts talking about the imminent arrival of the God Battery, however, some important caveats. Most of the technical details remain secret. The energy-density claims have yet to be independently verified. Turning a tiny prototype cell into a road-worthy car battery is a huge and uncertain undertaking. And the battery industry has a proud, century-long tradition of overpromising and underdelivering.
For what it’s worth, Sastry seems to understand all of this. “We’ve had several cells and runs that have demonstrated these numbers to the point that we’re confident,” Sastry says.
For all its secrecy, Sakti3 is not an unknown quantity. If, in the past six or seven years, you’ve interacted with anyone at General Motors involved with the Chevy Volt, you’ve heard about Sastry and Sakti3. The story has always been this: Sakti3 is working on this new solid-state technology that could leapfrog lithium-ion—but that’s all I can tell you. By now the company has received millions in funding from backers including Khosla Ventures and GM Ventures, the automaker’s tech-investment arm. Jon Lauckner, the former General Motors executive who was the brains behind the Chevy Volt, and who now leads GM Ventures, sits on Sakti3’s board.
The company grew out of the engineering department of the University of Michigan. Sometime in 2006, Sastry and her colleagues began doing complex mathematical optimization schemes trying to figure out which of the many competing variables that go into an electric car battery—energy, power, mass, volume, cost, safety—could give. Their calculations told them to get rid of the liquid electrolyte found in conventional lithium-ion batteries, along with all of the extra packaging that a liquid electrolyte entails.
It’s easy to see why. The electrolyte in a lithium-ion battery is a liquid not unlike gasoline, and it’s responsible for many of the secondary chemical reactions that over time degrade batteries or, worse, cause meltdowns and fires. Because of the delicacy of the liquid electrolyte, lithium-ion battery packs used in cars are often shrouded in packaging—liquid cooling tubes, electronic controls, and so on. Those things add cost and weight.
But it’s not easy to get rid of the electrolyte. People have tried. Notable failures include the Canadian company Avestor, which filed for bankruptcy in 2006 after the solid-state lithium batteries it sold AT&T began detonating inside U-Verse cable boxes around North America.
Avestor used a polymer separator to replace the electrolyte in its batteries. We don’t know what Sakti3 is using—that’s a trade secret. The composition of the positive electrode also remains a secret; Sastry says it is nothing unusual—“a very well understood electrochemistry.” We do know that, like most of the promising post-lithium-ion battery chemistries identified so far, the Sakti3 battery has a metallic-lithium anode, or negative electrode.
The vacuum deposition process Sakti3 uses to manufacture its cells is significantly different from the lamination process most battery makers use. Lithium-ion battery factories look like a combination between a printing press and an industrial bakery. In huge industrial mixers, chemical powders are blended into a wet slurry; that gets coated onto sheets of metallic film, which is then chopped into electrodes, which are placed in pouches with the electrolyte and other components.
In the solid-state manufacturing process, by contrast, the layers of the thin-film battery are deposited sequentially—first the cathode, then the current collector, then the interlayer, anode, and so on. The entire process takes place in a vacuum chamber.
It’s not immediately apparent how working in a vacuum chamber could ever be cheap, but Sastry says there are cost benefits. “First, solid-state does not have any aging requirement. Cells come out fully charged and ready to test, where with the incumbent technology cells need 30 to 60 days” before you can use them. “Next, it’s very high throughput.” The manufacturing rate, she says, crippled earlier solid-state-battery efforts. “When we started there were a number of solid-state batteries in the literature,” she says. “They were made exclusively on platforms that would always be expensive due to the rate. Our numerical simulations told us to restrict our efforts to cheap tooling,” like the custom prototype line the company is using today.
Sakti3 also benefits from the passage of time. They get to take advantage of the huge amount of engineering that has gone into manufacturing processes for solar panels, flat-panel displays, and other solid-state electronics. “While we were working on our technology there were significant advances in cost in technologies that are very similar to ours,” Sastry says. “We will benefit from those.”
All of this, she says, is why Sakti3 should eventually be able to hit that goal of $100 per kilowatt-hour.
There are plenty of other variables to consider. What about cycle life—that is, the number of times the battery can be charged and discharged before it starts to become worthless? Sastry says that because the chemical reactions in her cells are much simpler than those in conventional lithium-ion batteries, they should last longer. “We expect great cycle life.” What about safety? “Solid state eliminates the riskiest part of the battery cell,” she says. “You can snap one of the batteries into two pieces. Drop hot solder on it and it continues to operate.”
One of the few experts privy to the details of Sakti3’s work is Wei Lu, a professor of engineering at the University of Michigan. Lu says he has no direct involvement with Sakti3 and no financial ties to the company. He also says he is impressed. “They have a very rigorous testing facility,” he says. “Their results are highly impressive and very accurate.”