SAN JOSE, Calif. — For years, scientists in laboratories from Silicon Valley to Boston have been searching for an elusive potion of chemicals, minerals and metals that would allow electric vehicles to recharge in minutes and travel hundreds of miles between charges, all for a much lower cost than batteries available now.

Now a few of those scientists and the companies they founded are approaching a milestone. They are building factories to produce next-generation battery cells, allowing carmakers to begin road testing the technologies and determine whether they are safe and reliable.

The factory operations are mostly limited in scale, designed to perfect manufacturing techniques. It will be several years before cars with the high-performance batteries appear in showrooms, and even longer before the batteries are available in moderately priced cars. But the beginning of assembly-line production offers the tantalizing prospect of a revolution in electric mobility.

If the technologies can be mass-produced, electric vehicles could compete with fossil-fuel-powered vehicles for convenience and undercut them on price. Harmful emissions from automobile traffic could be substantially reduced. The inventors of the technologies could easily become billionaires — if they aren’t already.

For the dozens of fledgling companies working on new kinds of batteries and battery materials, the emergence from cloistered laboratories into the harsh conditions of the real world is a moment of truth.

Producing battery cells by the millions in a factory is vastly more difficult than making a few hundred in a clean room — a space designed to minimize contaminants.

“Just because you have a material that has the entitlement to work doesn’t mean that you can make it work,” said Jagdeep Singh, founder and chief executive of QuantumScape, a battery maker in San Jose, Calif., in the heart of Silicon Valley. “You have to figure out how to manufacture it in a way that’s defect-free and has high enough uniformity.”

Adding to the risk, the slump in tech stocks has stripped billions of dollars in value from battery companies that are traded publicly. It will not be as easy for them to raise the cash they need to build manufacturing operations and pay their staff. Most have little or no revenue because they have yet to begin selling a product.

QuantumScape was worth $54 billion on the stock market shortly after it went public in 2020. It was recently worth about $4 billion.

That has not stopped the company from forging ahead with a factory in San Jose that by 2024, if all goes well, will begin producing cells for sale. Automakers will use the factory’s output to test whether the batteries can withstand rough roads, cold snaps, heat waves and carwashes.

The automakers will also want to know if the batteries can be recharged hundreds of times without losing their ability to store electricity, whether they can survive a crash without bursting into flames and whether they can be manufactured cheaply.

It’s not certain that all the new technologies will live up to their inventors’ promises. Shorter charging times and longer range may come at the expense of battery life span, said David Deak, a former Tesla executive who is now a consultant on battery materials. “Most of these new material concepts bring huge performance metrics but compromise on something else,” Mr. Deak said.

Still, with backing from Volkswagen, Bill Gates and a who’s who of Silicon Valley figures, QuantumScape illustrates how much faith and money have been placed in companies that claim to be able to fulfill all those requirements.

Mr. Singh, who previously started a company that made telecommunications equipment, founded QuantumScape in 2010 after buying a Roadster, Tesla’s first production vehicle. Despite the Roadster’s notorious unreliability, Mr. Singh became convinced that electric cars were the future.

“It was enough to provide a glimpse of what could be,” he said. The key, he realized, was a battery capable of storing more energy, and “the only way to do that is to look for a new chemistry, a chemistry breakthrough.”

Mr. Singh teamed up with Fritz Prinz, a professor at Stanford University, and Tim Holme, a researcher at Stanford. John Doerr, famous for being among the first investors in Google and Amazon, provided seed money. J.B. Straubel, a co-founder of Tesla, was another early supporter and is a member of QuantumScape’s board.

After years of experimentation, QuantumScape developed a ceramic material — its exact composition is a secret — that separates the positive and negative ends of the batteries, allowing ions to flow back and forth while avoiding short circuits. The technology makes it possible to substitute a solid material for the liquid electrolyte that carries energy between the positive and negative poles of a battery, allowing it to pack more energy per pound.

“We spent about the first five years in a search for a material that could work,” Mr. Singh said. “And after we thought we found one, we spent another five years or so working on how to manufacture it in the right way.”

Though technically a “pre-pilot” assembly line, the QuantumScape factory in San Jose is almost as big as four football fields. Recently, rows of empty cubicles with black swivel chairs awaited new employees, and machinery stood on pallets ready to be installed.

In labs around Silicon Valley and elsewhere, dozens if not hundreds of other entrepreneurs have been pursuing a similar technological goal, drawing on the nexus of venture capital and university research that fueled the growth of the semiconductor and software industries.

Another prominent name is SES AI, founded in 2012 based on technology developed at the Massachusetts Institute of Technology. SES has backing from General Motors, Hyundai, Honda, the Chinese automakers Geely and SAIC, and the South Korean battery maker SK Innovation. In March, SES, based in Woburn, Mass., opened a factory in Shanghai that is producing prototype cells. The company plans to begin supplying automakers in large volumes in 2025.

SES shares have also plunged, but Qichao Hu, the chief executive and a co-founder, said he wasn’t worried. “That’s a good thing,” he said. “When the market is bad, only the good ones will survive. It will help the industry reset.”

SES and other battery companies say they have solved the fundamental scientific hurdles required to make cells that will be safer, cheaper and more powerful. Now it’s a question of figuring out how to churn them out by the millions.

“We are confident that the remaining challenges are engineering in nature,” said Doug Campbell, chief executive of Solid Power, a battery maker backed by Ford Motor and BMW. Solid Power, based in Louisville, Colo., said in June that it had installed a pilot production line that would begin supplying cells for testing purposes to its automotive partners by the end of the year.

Indirectly, Tesla has spawned many of the Silicon Valley start-ups. The company trained a generation of battery experts, many of whom left and went to work for other companies.

Gene Berdichevsky, the chief executive and a co-founder of Sila in Alameda, Calif., is a Tesla veteran. Mr. Berdichevsky was born in the Soviet Union and emigrated to the United States with his parents, both electrical engineers on nuclear submarines, when he was 9. He earned bachelor’s and master’s degrees from Stanford, then became the seventh employee at Tesla, where he helped develop the Roadster battery.

Tesla effectively created the E.V. battery industry by proving that people would buy electric vehicles and forcing traditional carmakers to reckon with the technology, Mr. Berdichevsky said. “That’s what’s going to make the world go electric,” he said, “everyone competing to make a better electric car.”

Sila belongs to a group of start-ups that have developed materials that substantially improve the performance of existing battery designs, increasing range by 20 percent or more. Others include Group14 Technologies in Woodinville, Wash., near Seattle, which has backing from Porsche, and OneD Battery Sciences in Palo Alto, Calif.

All three have found ways to use silicon to store electricity inside batteries, rather than the graphite that is prevalent in existing designs. Silicon can hold much more energy per pound than graphite, allowing batteries to be lighter and cheaper and charge faster. Silicon would also ease the U.S. dependence on graphite refined in China.

The drawback of silicon is that it swells to three times its size when charged, potentially stressing the components so much that the battery would fail. People like Yimin Zhu, the chief technology officer of OneD, have spent a decade baking different mixtures in laboratories crowded with equipment, looking for ways to overcome that problem.

Now, Sila, OneD and Group14 are at various stages of ramping up production at sites in Washington State.

In May, Sila announced a deal to supply its silicon material to Mercedes-Benz from a factory in Moses Lake, Wash. Mercedes plans to use the material in luxury sport utility vehicles beginning in 2025.

Porsche has announced plans to use Group14’s silicon material by 2024, albeit in a limited number of vehicles. Rick Luebbe, the chief executive of Group14, said a major manufacturer would deploy the company’s technology — which he said would allow a car to recharge in 10 minutes — next year.

“At that point all the benefits of electric vehicles are accessible without any disadvantages,” Mr. Luebbe said.

Demand for batteries is so strong that there is plenty of room for multiple companies to succeed. But with dozens if not hundreds of other companies pursuing a piece of a market that will be worth $1 trillion once all new cars are electric, there will surely be failures.

“With every new transformational industry, you start with a lot of players and it gets narrowed down,” Mr. Luebbe said. “We will see that here.”