Inside the Massachusetts start-up racing to transform EVs — and the world — with solid-state batteries.

On a bitterly cold morning this January in Billerica, Massachusetts, Siyu Huang received a brief text that marked a major milestone in her life’s work.

“Spinning wheels,” it read.

Attached was a short video clip. It showed a car on rollers in a lab — unremarkable at first glance. But this was no ordinary emissions test. The car had no tailpipe. And for Huang, CEO of Factorial Energy, it was proof that a decade of research had finally produced a functioning solid-state battery capable of powering an actual vehicle.

The video came from Uwe Keller, head of battery development at Mercedes-Benz, one of several major automakers backing Factorial. It showed that Factorial’s experimental battery had been installed in a Mercedes sedan — and it worked. The wheels were turning.

That simple moment in a Stuttgart lab marked a major leap forward for a technology that could help end the era of gasoline-powered cars.

A Battery With Global Stakes

Factorial Energy is one of dozens of companies pursuing a holy grail in clean transportation: solid-state batteries that charge faster, last longer, weigh less, and are safer than the lithium-ion batteries in today’s electric vehicles.

Transportation remains the largest source of greenhouse gas emissions in the U.S., and EVs are a critical tool in the fight against climate change. A breakthrough battery would not only make EVs cheaper and more convenient — potentially tipping global car markets — but could also give the U.S. and Europe a rare edge over China in a technology race they’ve largely trailed so far.

For Huang and her team, the Mercedes test was the first tangible proof that their design could power a real car — not just a lab prototype. “We’re car guys,” said Keller. “We believe in things really moving.”

From Nanjing to Billerica

Huang’s journey to that moment began in Nanjing, China, where as a child she gathered environmental data for a school science program. The air pollution around her sparked a lifelong interest in chemistry — and in fixing what she saw as a planetary health crisis.

She later studied at Xiamen University and earned a spot in a Swedish exchange program. Afterward, she and her future husband, Alex Yu, were both accepted to Ph.D. programs at Cornell University. She arrived in Ithaca, New York, in 2009 with just $3,000 in savings from her scholarship. The couple eventually became U.S. citizens.

At Cornell, Huang and Yu studied electrochemistry under Professor Héctor Abruña, a leading researcher in the field. With an idea born in Abruña’s lab — and some seed funding from New York State — they co-founded what would become Factorial Energy while Huang was still completing her M.B.A. at Cornell.

“They’re extremely bright and extremely dedicated,” said Abruña. “Straight shooters — zero BS.”

Yu is now the company’s chief technology officer. Their operation is still relatively small, with just over 100 employees. Huang, calm and analytical, leads from a modest office overlooking a patch of forest in suburban Massachusetts. Her diplomas from Cornell — a Ph.D. in chemistry and an M.B.A. — hang on the wall. She doesn’t boast about sleepless nights. “Having a clear mind to make the right decision is more important than how many hours you work,” she said.

A Shift to Solid-State

Factorial originally focused on improving lithium-ion batteries. That changed after Mercedes invested in the company in 2021. The automaker wanted to leap ahead of rivals and saw solid-state technology as the key.

Unlike traditional batteries, which use a liquid electrolyte to shuttle ions, solid-state batteries use a solid or gelatinous material. Eliminating the flammable liquid can reduce fire risk and enable faster charging. Solid-state batteries also offer more energy density, which could mean lighter cars with longer ranges.

But there’s a catch: solid-state cells are notoriously tricky. They’re prone to dendrites — spiky metal formations that cause short circuits and battery failure. Dozens of companies are chasing solutions, but none have yet brought solid-state EVs to market. Even if some automakers have quietly tested them, no one has proven the tech can reliably survive real-world conditions.

In late 2023, Keller proposed that Mercedes test Factorial’s battery in an actual vehicle — a bold move that pushed the technology out of the lab and into the garage. The first results were promising.

“There’s still a long way to go,” said Huang. The car hadn’t yet been driven on public roads — the ultimate test. But the wheels were spinning.

The Road Ahead

If Factorial succeeds, it won’t just mean a better battery — it could help reshape the global auto industry. Solid-state batteries could render internal combustion engines obsolete and give the West a technological edge in a field where China dominates supply chains and raw materials.

Factorial’s challenge is not only to perfect the chemistry but to ensure its batteries can be manufactured at scale. Vast rewards await the first company to solve the safety and durability problems — and make batteries that are not just lab-ready, but road-ready.

For now, Huang remains focused and cautiously optimistic. The path from spinning wheels in a lab to millions of cars on real highways is long and uncertain. But after ten years of work, her invention is finally moving forward — literally.