A decade-long search for a battery that can end the gasoline era

Boston Globe

12-05-2025

Huang, her husband, Alex Yu, and their employees at Factorial had been working on a new kind of electric vehicle battery, known as solid state, that could turn the auto industry on its head — if a daunting number of technical challenges could be overcome.
For Huang and her company, the battery had the potential to change the way consumers think about electric vehicles, give the United States and Europe a leg up on China, and help save the planet.
Factorial is one of dozens of companies trying to invent batteries that can charge faster, go farther, and make electric cars cheaper and more convenient than gasoline vehicles. Electric vehicles could be a potent weapon against climate change and urban air pollution.
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The video that landed in Huang's phone was from Uwe Keller, the head of battery development at Mercedes-Benz, which had been supporting Factorial's research with money and expertise.
The short clip, of a Mercedes sedan at a research lab near Stuttgart, Germany, signaled that the company had installed Factorial's battery in a car — and that it could actually make the wheels move.
The test was an important step forward in a journey that had begun while Huang and Yu were still graduate students at Cornell University. Until then, all their work had been in laboratories. Huang was excited that their invention was venturing into the world.
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But there was still a long way to go. The Mercedes with a Factorial battery hadn't yet been taken out on the road.
Many startups have produced solid-state battery prototypes. But no American or European carmaker has put one into a production vehicle and proved that the technology could survive the bumps, vibrations and moisture of the streets.
In late 2023, Keller, a veteran Mercedes engineer, proposed to Huang that they try.
'We're car guys,' Keller said later. 'We believe in things really moving.'
Huang stands out in a niche dominated by men from Silicon Valley. Some brag about their 100-hour workweeks; she believes in a good night's sleep. 'Having a clear mind to make the right decision is more important than how many hours you work,' she said.
Huang grew up in Nanjing, China, where she was in an elementary school program that had her gather environmental data. The program instilled an interest in chemistry and an awareness of the vehicle exhaust and industrial pollution choking Nanjing's air. She realized, she recalled, that 'we need to grow a planet that's healthier for human beings.'
In a dormitory at Xiamen University on China's southern coast, where she studied chemistry, she saw an advertisement for a Swedish exchange program. After spending two years there, she and Alex were both accepted to doctoral programs in Cornell's chemistry department. She arrived in Ithaca, N.Y., in 2009. They have both since become US citizens.
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Yu is now Factorial's chief technology officer. The company is, in that sense, a family operation.
Initially the company focused on improving the materials that allow batteries to store energy. That changed after Mercedes invested in Factorial in 2021. Mercedes was looking for a bigger technological leap and encouraged Factorial to pursue solid state.
The technology has that name because it eliminates the liquid chemical mixture, known as an electrolyte, that helps transport energy-laden ions inside a battery. Liquid electrolytes are highly flammable. Replacing them with a solid or gelatinlike electrolyte makes batteries safer.
A battery that doesn't overheat can be charged faster, perhaps in as little time as it takes to fill a car with gasoline. And solid-state batteries pack more energy into a smaller space.
But solid-state batteries have one big drawback: Such battery cells are more prone to grow spiky irregularities that cause short circuits. Vast riches await any company that can overcome this problem and develop a battery that is durable, safe and reasonably easy to manufacture at a reasonable price.
Factorial confronted that problem in 2022, setting up a small pilot factory in Cheonan, South Korea, a city near Seoul known for its tech industry. The project became, in Huang's words, 'production hell.'
To make money, a battery factory can't produce too many defective cells. Ideally the yield, the percentage of usable cells, should be at least 95 percent. Hitting that target is devilishly difficult, involving volatile chemicals and fragile separators layered and packaged into cells with zero margin for error.
In the beginning, Factorial's prototype assembly line in South Korea had a yield of just 10 percent, meaning 90 percent of its batteries were faulty.
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'There were always issues,' Huang said. 'There was a point, I was like, I don't even know if we can make it.'
By 2023, Factorial had produced enough cells suitable for an automobile that Keller began thinking about installing them in a car. Keller went to Ola Källenius, the Mercedes CEO, who signed off on the project.
Huang was a bit surprised when, in late 2023, Keller told her that Mercedes wanted to put the cells in a working vehicle. 'We didn't realize it was coming so soon, honestly speaking,' she said.
But by June 2024, Factorial had managed to produce enough high-quality cells to announce that it had begun delivering them to Mercedes. In November, the factory in South Korea hit 85 percent yield, the best result yet.
Mercedes still had to figure out how to package the cells in a way that would protect them from highway dirt and moisture. And it had to integrate the battery pack into a vehicle, connecting it to the car's control systems.
By Christmas 2024, a team working at Mercedes' main research center outside Stuttgart texted Keller those two words: 'spinning wheels.'
Keller confessed that he got emotional when his team sent him the video of the car. He waited until after Christmas to forward it to Huang with the same two words.
Several weeks later, the Mercedes engineers took the car with Factorial's battery, an otherwise standard EQS electric sedan, to a company track for its first road test.
The engineers drove the car slowly at first. They carefully monitored technical data displayed on the dashboard screen.
They drove faster and faster until, by the fourth day, they reached 100 mph. The battery didn't blow up. In theory, it can power the car for 600 miles.
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The next step is to equip a fleet of Mercedes vehicles with batteries, perfect the manufacturing process and do the testing required to begin selling them. That will probably take until 2028, at least. Many experts don't expect cars with solid-state batteries to be widely available until 2030, at the earliest.
In April, Huang finally found time to travel to Stuttgart and ride in the car herself.
Huang had seen many photos of the car, but she still felt a thrill when the garage doors opened. It felt 'like a long-lost friend,' she said. 'Like, 'Finally I see you!''
A Mercedes driver took her for a spin on the test track.
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