ProLogium starts mass production of a 381 Wh/kg battery density: automakers are still waiting

Solid-state electrolyte batteries, also known as solid-state, have been talked about for years as a solution that would instantly boost both range and safety in electric vehicles. Taiwanese ProLogium, which Mercedes-Benz has invested in, has now announced that it is already producing them in series—and with specs that beat anything currently driving in cars. Automakers, however, aren’t rushing in.

381 Wh/kg and 903 Wh/l, verified by a third party

This is about the 3.5 generation ceramic lithium battery. It’s a large-format cell with a capacity of 185.4 Ah, which—according to TÜV Rheinland measurements—reached a gravimetric energy density of 381 Wh/kg and a volumetric energy density of 903 Wh/l. For comparison, typical cells in today’s electric cars are far lower—which is why this figure is closely watched in the industry.

The second test was carried out by UL Solutions under China’s standard GB/T 43568-2026, which defines what may be called a fully solid-state electrolyte battery. After six hours in a vacuum at 120 °C, the cell lost less than 0.05% of its mass, while the standard allows up to 0.5%. Based on China’s methodology, this is therefore a real all-solid-state battery—not a semi-solid intermediate step that several manufacturers offer today.

Production is running, but there’s simply far too little of it

That’s where the hype starts to break. The line in Taiwan’s Tchao-jüan has an annual capacity of 0.5 GWh. With roughly 80 kWh batteries, that works out—at least theoretically—to about 6,250 cars per year. It’s the kind of number any automaker could use up in just a few days of producing a single model.

The company isn’t starting from zero, though. It already had a first sample line with a capacity of 10 MWh back in 2013, four years later it moved to pilot production with 40 MWh, and today it’s at the gigawatt-hour level. Altogether, according to its own figures, it has delivered more than 2.4 million cells across consumer electronics, special applications, and the automotive sector, including around 10,000 samples directly for automakers.

A big leap is expected from Dunkerque

In Taiwan, ProLogium wants to scale capacity to one to two gigawatt-hours. The real volume, however, is set to come from the plant in France—Dunkerque—whose first phase targets 4 GWh, with intended capacity reaching up to 44 GWh by 2030.

This European location is crucial for the whole story. Solid-state electrolyte batteries are developed today mostly in China, Japan, and Korea, while Europe lags behind in this area. A plant in northern France would create a manufacturing base on the old continent—one that no one else has here yet.

Why automakers aren’t rushing in

The reason is primarily economic. As the portal CarNewsChina points out, cheap LFP cells for the mass market in China cost roughly 300 to 400 yuan per kilowatt-hour, which works out to about 36 to 48 euros. ProLogium hasn’t disclosed the price of its 3.5 generation, and with such a small series it’s guaranteed to be several times higher. On top of that comes a technical unknown: energy density at the cell level doesn’t necessarily guarantee the same advantage once the cell is packaged into a complete battery with cooling, structure, and the control electronics.

ProLogium also has relationships with automakers. An agreement on technology collaboration links it with Mercedes-Benz; it also worked on R&D and sample projects with Chinese brands Nio and Aiways. From the agreement to a series car, however, is still a long way off—and nobody is in a hurry to announce a specific model yet.

BYD and CATL promise years 2027 to 2030

Other players are more cautious in their schedule. BYD plans a small demo series in 2027—on the order of thousands of units—aimed at premium models with a range of over 1,200 kilometers, and it pushes actual mass production all the way to 2030. CATL also talks about small batches starting in 2027. ProLogium therefore has an edge in that it is already producing something—though in a volume that is not enough for anyone so far.

For buyers in Slovakia, this currently means nothing concrete. The cars you can pick up from a dealer today run on LFP or NMC cells, and that will remain the case for a few years—solid-state electrolyte batteries will first show up in expensive models, and only then, if at all, in the mainstream class. What changes sooner is the terminology in price lists: the term “solid-state” is already being used by manufacturers even where it’s only a semi-solid electrolyte—and the difference between that and a true solid battery is crucial.

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