Global auto-making giant Stellantis N.V. said it plans to spend more than $35.5 billion through 2025 to release an array of new plug-in models, the company’s boldest statement yet on how it plans to compete in the industry’s intensifying electric-vehicle race.

The car company, formed earlier this year through the merger of Fiat Chrysler Automobiles N.V. and France’s PSA Group, also plans to get more involved with battery development and sourcing, aiming to drive down costs on one of the most expensive components for an electric car.

Executives said Thursday its strategy would support the establishment of five battery factories in North America and Europe and it aims to offer electrified options under all 14 of its brands, which include Jeep, Ram, Peugeot and Citroën. Among the new models planned are an electric Ram truck, expected to arrive in 2024, and an electric Dodge muscle car to be released that same year.

“This electrification journey is possibly the most important brick in our long-term plan,” said Chief Executive Carlos Tavares during a presentation to analysts and journalists.

The company’s rollout of its plans did little to excite investors. Stellantis shares slid 2.6% to $19.10 in midday trading.

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In recent months, other major car companies have upped their bets on electric vehicles as tougher tailpipe-emissions regulations globally are prodding manufacturers to pivot from their more-than-century-old model of selling gasoline-powered vehicles. The move is also being driven by rising enthusiasm on Wall Street for the technology as investors look to bet on the next Tesla Inc.

Several weeks ago, General Motors Co. increased its planned spending on electric and autonomous vehicles—its second boost in less than a year—raising it to $35 billion through 2025. The increase reflects the addition of two more battery factories, on top of ones already planned for Ohio and Tennessee.

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Ford also has become more aggressive, unveiling in May an all-electric version of its bestselling vehicle, the F-150 truck. It plans to invest $30 billion in electric vehicles through 2025.

Meanwhile, Volkswagen AG is spending about $40 billion through mid-decade on electric vehicles.

Jefferies analyst Philippe Houchois said that while Stellantis’s presentation provided some key details about its plans, it still felt similar to what others already have in the works and in some areas, the company appeared behind. For instance, the electric Ram pickup truck isn’t set to arrive until 2024, long after many key rivals, he said. Ford plans to release its electric F-150 Lightning next year.

“They have ambitions which are shared with everyone in the industry,” he said. “They claim they will do it more cheaply, which is great, but we are going to see.”

Mr. Tavares, who took the top job at Stellantis in January upon the merger’s completion, has made providing a clear path forward on electric vehicles a priority for the newly formed company.

Earlier this year, the company pledged to offer an electrified version of almost every model in its lineup by 2025. On Thursday, it said by 2030, 70% of its vehicle sales in Europe and more than 40% of its sales in the U.S. will be electric models—targets that analysts say are among the industry’s most ambitious.

Still, Stellantis has been widely seen by analysts as lagging behind many of its competitors on electric vehicles, in part because Fiat Chrysler had been slower to invest in the technology before the tie-up and its lineup is more tilted toward muscle cars and heavier trucks and sport-utility vehicles.

Executives have promoted the merger as giving both companies the scale and resources needed to compete in a sector where investment in costly new technologies, such as battery-powered cars, has become a necessity. Stellantis has said the merger is expected to deliver $6 billion in savings annually, much of which will be spent on efforts to add more plug-in models to its lineup.

On Thursday, Stellantis executives outlined plans to electrify different sizes and types of vehicles, ranging from small cars to big trucks and SUVs sold under its Jeep brand. It also said it plans to offer two kinds of battery chemistries, a high-density option and a nickel cobalt-free alternative by 2024, as well as introduce solid-state battery technology by 2026.

A Chrysler Pacifica minivan under assembly in Windsor, Ontario, in 2018.

A Chrysler Pacifica minivan under assembly in Windsor, Ontario, in 2018.

Photo: rebecca cook/Reuters

The company plans to establish the battery factories through supplier partnerships, and in some cases it expects to use its existing manufacturing facilities for the production. For instance, in Italy it is converting one engine factory to make electric-car batteries, Mr. Tavares said.

The car company also previewed its financial results for the first half of the year Thursday. The company said its adjusted operating margins for the first six months of 2021 should be above its full-year guidance range of 5.5% to 7.5%, due to higher pricing and it selling a more profitable mix of models.

Jeep is part of Stellantis, formed by the PSA-Fiat Chrysler combination.

Jeep is part of Stellantis, formed by the PSA-Fiat Chrysler combination.

Photo: Gian Mattia D\'Alberto/Zuma Press

Stellantis said it expects free cash flow in the same period to be negative, attributing the results to lower planned production volumes as the auto industry grapples with a computer-chip shortage that is curtailing factory output.

Stellantis’s two biggest car markets—Europe and the U.S.—are expected to tighten regulations limiting tailpipe emissions in the coming years, putting pressure on the company to lessen its reliance on gasoline-powered vehicles. Governments are also offering more incentives to get auto makers to invest in electrics.

In the U.S., President Biden has called for $174 billion in electric-vehicle-related spending, which includes fresh federal tax credits for purchasing plug-in cars and commercial trucks.

Meanwhile, other car companies are moving quickly to put out electric vehicles and the marketplace is becoming more crowded, with startups such as Rivian Automotive and Lucid Motors Inc. moving closer to selling their first plug-in models. Tesla continues to expand globally and fortify its grip on the market with growing sales and new-model debuts.

Stellantis needs to prove to investors the company’s ambitions are backed up by models that will be ready in the near-term and on a timeline that is on par with industry rivals, Mr. Houchois said.

A Paris showroom for Peugeot, also part of Stellantis.

A Paris showroom for Peugeot, also part of Stellantis.

Photo: Cyril Marcilhacy/Bloomberg News

Write to Nora Naughton at Nora.Naughton@wsj.com