Scientists now know why solid-state batteries have repeatedly failed. Two separate studies have identified the physical processes responsible for the short circuits that have delayed commercialization for years, turning one of the industry’s biggest unknowns into a defined engineering problem. For years, engineers knew how solid-state batteries were failing, but not why.

The batteries repeatedly developed internal short circuits as microscopic lithium structures formed inside the cell and eventually pierced the barrier separating the battery’s positive and negative sides. Researchers could see what was happening after the fact, but they couldn’t explain what caused those structures to form or how they managed to penetrate a material specifically designed to block them. Two independent research teams have now answered different parts of that question.

In a paper published in Nature, scientists at Germany’s Max Planck Institute for Sustainable Materials found that lithium deposits generate enormous internal pressure during charging, eventually cracking the solid electrolyte from within. Separately, researchers from MIT, the Technical University of Munich, and collaborating institutions reported in Nature Nanotechnology that tiny electrical imbalances inside the electrolyte create the conditions that allow the unwanted lithium structures to begin growing. The findings could remove a major scientific uncertainty just as automakers and battery manufacturers are investing billions of dollars to bring solid-state batteries into commercial production.

Manufacturers Aren’t Waiting Around Solid-state batteries are widely regarded as the next major advance in battery technology because they promise to deliver longer driving ranges, faster charging, improved safety, and higher energy density than today’s lithium-ion batteries. Replacing the liquid electrolyte with a solid material also reduces the risk of overheating and allows manufacturers to pack more energy into the same physical space, making the technology attractive not only for EVs, but also for aviation, defense, and grid-scale energy storage. Related: Europe's Heatwave Is Becoming an Energy Crisis The repeated failures never convinced the auto industry that solid-state batteries were unworkable.

Instead, manufacturers chose to view them as engineering problems that could be solved eventually. The prize was simply too large to ignore because, compared with today’s lithium-ion batteries, solid-state promises higher energy density, faster charging, improved safety, and longer driving ranges. Manufacturers appear convinced that solid-state is what will completely reshape the EV industry.

Manufacturers have turned that faith into billions of dollars in investment. Honda has already built a demonstration production line to develop the manufacturing techniques needed for mass production. Toyota continues targeting commercial deployment later this decade, while Mercedes-Benz, BMW, Stellantis, Hyundai, Samsung SDI, CATL, QuantumScape, Solid Power, and Factorial Energy have all expanded pilot production, strategic partnerships, or vehicle testing programs despite the technology’s unresolved scientific challenges.