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.

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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.

Honda has spent approximately $280 million on a 27,400-square-meter solid-state battery production line in Sakura City, Japan. The facility replicates the full manufacturing process, from mixing and coating electrode materials through cell formation and module assembly. Battery production was scheduled to begin in January 2025, with Honda testing production costs, cell specifications, and mass-manufacturing methods ahead of vehicle deployment in the second half of the decade.

Honda is using roll-pressing to compress the solid electrolyte during assembly, reducing microscopic air gaps that impede ion transport while simplifying large-scale manufacturing. The company is also developing thinner cooling systems made possible by the greater thermal stability of solid-state batteries, reducing both battery weight and manufacturing complexity.

Mercedes-Benz has already put a solid-state battery on public roads. Earlier this year, the company unveiled a modified EQS equipped with lithium-metal cells supplied by Factorial Energy. During testing, the vehicle traveled 1,205 kilometers between Stuttgart and Malmö on a single charge and finished the journey with 137 kilometers of estimated range remaining.

BMW is testing large-format Solid Power cells in an i7 on public roads around Munich. The program is examining cell expansion, operating pressure, and temperature control inside a complete vehicle pack. BMW has also licensed Solid Power’s production technology for a prototype cell line at its Cell Manufacturing Competence Center in Parsdorf. 

Idemitsu is constructing a large pilot facility to manufacture sulfide solid electrolytes, one of the most important elements of Toyota’s next-generation batteries. The plant will produce lithium sulfide using sulfur recovered from petroleum refining before converting it into solid electrolyte material for automotive batteries. Toyota plans to begin commercial production of vehicles using the technology during 2027-2028.

What’s Next?

The solid-state mystery has been replaced with a design problem. 

Researchers now know that preventing electrolyte fractures and suppressing localized current concentrations will determine whether solid-state batteries can survive repeated charging cycles outside the laboratory.

But commercialization isn’t a given. Once the now-known problems are engineered out, it will be up to manufacturers to prove that solid-state batteries can be produced consistently at automotive scale, withstand thousands of charging cycles, and reach cost levels that compete with today’s lithium-ion batteries. That’s why companies continue to invest hundreds of millions of dollars into pilot production lines years before mass-market vehicles arrive.

Toyota still expects to introduce its first solid-state batteries during 2027-2028. Honda is targeting the second half of the decade. Mercedes-Benz, BMW, and several battery manufacturers have already moved from laboratory cells to vehicles operating on public roads. This is about to become an industrial race. 

By Julianne Geiger for Oilprice.com

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