The battery, built by a California start-up, Sila, provided the tiny fitness tracker with more power than older batteries while maintaining the same battery life…

While he said this approach gave Sila a significant advantage over his many competitors, Dr. Viswanathan, the Carnegie Mellon professor, said other companies were taking different routes to refining the way lithium-ion batteries are built.

Companies like Sila and QuantumScape already have partnerships with carmakers and expect that their batteries will reach automobiles around the middle of the decade. They hope their technologies significantly reduce the cost of electric cars and extend their driving range.

“If we want to get electric cars into the mainstream, we have to get them down to the $30,000 price point,” said Mr. Singh, the QuantumScape chief executive. “You can’t do that with today’s batteries.”
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