ProLogium puts a 381 Wh/kg all-solid-state cell into mass production, but scale and cost tests lie ahead

ProLogium announced on September 2 that its Generation 3.5 Lithium Ceramic Battery has moved beyond the development stage, with a 185.4 Ah large-format cell rated at 381 Wh/kg and 903 Wh/L now in production. The Taiwanese firm has a technology cooperation agreement with Mercedes-Benz and has previously run solid-state development and sample-vehicle work with Nio and Aiways. TÜV Rheinland verified the density figures, while UL Solutions tested the cell under China's GB/T 43568-2026 all-solid-state methodology: after six hours in continuous vacuum at 120°C, mass loss came in under 0.05%, well inside the 0.5% threshold.

That certification carries weight because China's national solid-state standard, in force since July 2026, was created to separate genuine all-solid-state designs from semi-solid products that retain liquid electrolyte — a boundary drawn after SAIC-backed IM Motors promoted its "Light-Year" pack as solid-state despite containing liquid. Beijing has since submitted the standard to the IEC as a candidate reference for international rules.

The industrial picture is more modest than the headline number. The Taoyuan plant's initial 0.5 GWh capacity would cover only about 6,250 80-kWh packs a year, with expansion capped at 1-2 GWh for now; the planned Dunkirk factory in France — 4 GWh in its first phase, 44 GWh at maximum design — would be eight times the Taiwanese site but ramps only toward 2030. Of the 2.4 million cells shipped to date, more than 900,000 went to a U.S. audio-system supplier for a Japanese automaker's North American vehicles, alongside just around 10,000 automotive samples.

Cost remains the decisive unknown. Chinese LFP cells reportedly sell at the cell level for roughly 300-400 yuan (about $42-55) per kWh, and ProLogium has disclosed no comparable figure for the new cell. Until it demonstrates competitive cost, yield and pack-level performance, the 381 Wh/kg result stands as a cell-level milestone rather than proof of lighter EV battery packs — the reason carmakers are watching rather than committing.