When ProLogium started series production of a certified 381 Wh/kg solid-state cell on 7 September, the obvious question was who would buy them. The company named no carmaker.
It has now named one — for the generation after. Mercedes-Benz has secured first rights to ProLogium's Gen4 cell, the company's "Superfluidized Inorganic Lithium Ceramic" chemistry, for evaluation.
Read the two columns together
| Gen 3.5 | Gen4 | |
|---|---|---|
| Energy density | 381 Wh/kg, certified by TÜV Rheinland | up to 400 Wh/kg, claimed |
| Fast charge | not published | 5% to 80% in 6.4 minutes |
| Electrolyte | non-flammable inorganic, ceramic separator | same family |
| Status | mass production in Taiwan | pre-production, first call to Mercedes |
The gap between the columns is the story. The 381 Wh/kg figure was measured by a third party on a 185.4 Ah automotive-format cell — the hard version of the claim. The 400 Wh/kg and the 6.4 minutes are manufacturer numbers for a cell a carmaker has only just been handed to test.
"First rights" is not a supply contract
Mercedes has not agreed to buy anything. It has agreed to be first in the queue to evaluate, which is a meaningful position in a market where one supplier has the only publicly demonstrated solid-state mass-production line, and a cheap one to take.
The relationship is old enough to be credible: the two have worked together since 2016, through hybrid solid-state packs and pouch, prismatic and bi-polar formats. Mercedes expects its first production EV with solid-state cells in 2030. That is the date to hold on to — a target, four years out, for a cell now entering evaluation.
Where they would be built in Europe
Dunkerque, where ProLogium broke ground in February 2026. The company expects roughly 4 GWh a year there by 2030, growing afterwards.
Four GWh is tens of thousands of cars' worth of cells, not hundreds of thousands. Whatever 2030 looks like, it is not a solid-state Mercedes range — it is a solid-state Mercedes.
What this means for Tesla
Tesla has named no solid-state partner and no solid-state date. Its own cell supplier LG Energy Solution argued in August that large-format solid-state cells are about a decade away, precisely because scaling the format is where the chemistry fails — and ProLogium's certified cell is the most direct answer anyone has given to that objection.
So the competitive fact here is not the chemistry. It is the queue. For one supplier's next generation, Mercedes is now at the front of it and Tesla is not in it.
None of this changes a purchase decision in 2026, or in 2028. Tesla's advantage has never rested on having the best cell — it has rested on pack engineering, manufacturing cost and charging infrastructure, and a 400 Wh/kg cell in a rival's prototype does not touch any of the three.
What it does change is the shape of the argument about 2030. Until now, "solid-state is a decade away" was a defensible position for a company without a programme. A named carmaker, a named plant and a named year make it a claim that has to be defended rather than assumed.