Mercedes-Benz Advances Solid-State Battery Testing
Mercedes-Benz has begun road testing a new solid-state battery in a modified EQS sedan, marking a significant step toward extending electric vehicle ranges. The tests, which started in February 2025 in Germany, involve a battery developed in partnership with Factorial Energy. Known as the Solstice battery, it promises up to 80% higher energy density than current lithium-ion cells, according to company announcements.
This collaboration addresses key challenges in EV adoption, such as range anxiety and safety. Initial tests have shown a 25% range increase, with potential for up to 600 miles per charge. Officials from both companies emphasize the battery's safety and efficiency improvements, as detailed in Mercedes-Benz's official media release and Factorial's September 2024 press release.
Partnership Evolution and Key Collaborators
The partnership between Mercedes-Benz and Factorial Energy dates back to a 2021 joint development agreement. In 2022, they secured $200 million in funding, with Stellantis joining as a co-investor. Factorial delivered B-samples in June before 2025, and road tests commenced in February 2025, incorporating a patented battery pack design from Mercedes-AMG High Performance Powertrains.
Other collaborators include Hyundai, Kia and Karma Automotive. Factorial plans a merger with Cartesian Growth Corp. III, valuing the company at $1.1 billion and including a $100 million PIPE investment, as outlined in a recent SEC filing. These milestones highlight a network of industry players aiming to accelerate solid-state battery adoption.
Key dates include the 2021 agreement, 2022 investment, Factorial's Sept. 10, 2024, press release and the February 2025 tests. Involved companies feature Factorial Energy leading development, Mercedes-Benz handling integration, Stellantis providing investment, and Hyundai and Kia as additional partners.
Technical Breakthroughs in Battery Design
The Solstice battery employs a sulfide-based solid-state electrolyte and a dry coating process that eliminates hazardous solvents, allowing production on existing lithium-ion lines. Factorial CEO Siyu Huang told Reuters this innovation enhances scalability. The battery achieves 450 watt-hours per kilogram in gravimetric energy density, 80% higher than conventional lithium-ion cells, according to Factorial's claims reported in WardsAuto.
Tests in the EQS demonstrated a 1,200-kilometer (745-mile) range, based on Factorial's data cited by Electrek. It maintains stability above 90 degrees Celsius, reducing fire risks and cooling needs, as noted in IEEE Spectrum. Mercedes-Benz describes it as semisolid-state in some contexts, a distinction highlighted by IEEE Spectrum, and it resists thermal runaway for improved safety.
The battery offers a 50% weight reduction and 50% higher volumetric density. "Safer, lighter, more efficient and 25 percent longer range in the first vehicle: solid-state cell chemistry delivers higher energy density and weight reduction," Mercedes-Benz stated in its official release.
Factorial's Huang said: "Solstice embodies our team’s technology leadership and the potential of solid-state batteries to address the most significant hurdles for electric vehicle adoption," in the Sept. 10 release via WardsAuto.
Implications for EV Industry Trends
Solid-state batteries like Solstice could alleviate range anxiety and safety concerns by cutting vehicle weight and simplifying cooling systems, potentially lowering costs. This development aligns with broader industry efforts amid slowing EV sales, as reported by GreenCars. For instance, Chery is testing 800-mile cells for 2027, according to Electrek, while Mercedes draws on Formula One expertise from AMG for its battery packs.
Factorial's scalable production leverages 80% of existing gigafactory lines, per SEC filings, which could hasten commercialization. Sources indicate range gains of 25% to 80%, with Mercedes reporting 25% in pack tests and Factorial claiming up to 80% at the cell level, as covered in WardsAuto and Electrek. No major contradictions emerge, though IEEE Spectrum notes the semisolid-state classification suggests near-term viability.
Challenges and Future Commercial Path
Factorial targets automotive original equipment manufacturers by 2030, with Mercedes-Benz confirming semisolid-state batteries in EVs by then, according to InsideEVs. Huang told The New York Times that solid-state batteries could appear in EVs as early as 2027, a timeline reinforced in July 2025 executive statements and cited in Electrek. The merger with Cartesian Growth Corp. III provides funding for scaling, signaling investor confidence per the SEC filing.
Challenges persist, including the lack of independent tests verifying exact energy densities and varying timelines between 2027 and 2030. Cost details remain absent, and historical delays in similar technologies raise skepticism. Battery Wire's analysis views this as a genuine advance, but hype exceeds reality—Mercedes' 25% gains temper Factorial's 600-mile claims, suggesting cell-level promises may not fully translate to vehicles.
Looking ahead, independent validation could build trust and reshape the EV landscape by 2030. If regulatory hurdles and scaling issues cause delays, lithium-ion batteries will likely remain dominant longer. Success here could accelerate widespread adoption, making extended-range EVs more accessible and addressing key barriers to a sustainable automotive future.