ProLogium, a Taiwanese company established in 2006 and headquartered in Taoyuan, has begun producing a solid-state battery cell with an energy density of 381 watt-hours per kilogram, confirmed by TÜV, a respected German testing agency. This performance exceeds that of the top liquid battery currently available, the CATL Qilin, which has an energy density of approximately 255 watt-hours per kilogram. On September 24, 2026, ProLogium signed an agreement granting Mercedes priority access to its Gen4 battery cells. Before full integration, Mercedes will conduct tests in external labs to evaluate the cells' electrical, thermal, and safety performance. Although Mercedes and the Vietnamese automaker VinFast are shareholders in ProLogium, the company remains independent and has no financial ties to CATL, a major Chinese battery manufacturer. In France, ProLogium is constructing a large-scale battery factory, or "gigafactory," in Dunkerque. The project, initiated in February 2026, involves an investment of 5.2 billion euros. The first phase of the plant is expected to produce 4 gigawatt-hours of battery capacity annually by 2030, with the full capacity reaching up to 44 gigawatt-hours once fully operational. Solid-state batteries differ from traditional liquid batteries by using a solid electrolyte instead of a flammable liquid, which enhances safety and allows for more energy storage in the same volume. ProLogium's Gen4 cells, specifically reserved for Mercedes, are expected to reach up to 400 watt-hours per kilogram and can charge from 5% to 80% in just 6.4 minutes. However, these performance figures are currently measured in controlled laboratory settings using high-powered chargers and may not yet be achievable with standard public charging stations. Mercedes is not the only automaker investing in solid-state battery technology. Chinese automaker BYD plans to launch its first solid-state electric vehicle as early as 2027, while Geely aims to produce a Volvo model with a range of 1,000 kilometers. Chery, another Chinese automaker, has set an ambitious goal of 1,500 kilometers for one of its models. MG is focusing on semi-solid batteries, which are less advanced but already in production. Samsung SDI, a partner of BMW, plans to begin mass production of solid-state batteries in the second half of 2027. QuantumScape, supported by Volkswagen and Honda, also aims to bring solid-state batteries to market between 2027 and 2028. However, the real challenge lies in scaling up production to meet demand, ensuring affordability, and proving the durability of these batteries in real-world conditions—none of which have been fully achieved yet. ProLogium asserts that it is the only company globally with a fully operational mass production line for solid-state batteries. This claim, however, will need to be validated by actual production volumes. Mercedes has stated that its first solid-state electric vehicle will not be available until 2030, and it is also partnering with American company Factorial Energy on this front. Meanwhile, the Dunkerque gigafactory is expected to begin producing its first battery cells as early as 2027. The success of these efforts will determine whether the promises of solid-state batteries—superior safety, longer range, and faster charging—can be realized at scale in the near future.