Solid-state batteries are often seen as the future of energy storage because they can potentially store more energy and operate more safely than today’s lithium-ion batteries.
But there is still one major problem: they tend to lose capacity much faster than scientists would like.
Now, researchers from TU Wien, Humboldt University of Berlin, and Helmholtz-Zentrum Berlin have discovered a hidden chemical process that may help explain why these advanced batteries degrade so quickly.
Their findings, published in ACS Energy Letters, reveal that oxygen trapped inside the battery materials can slowly trigger damaging reactions during charging and discharging.
Unlike conventional lithium-ion batteries, solid-state batteries use solid materials instead of flammable liquid electrolytes. This makes them much safer and could allow electric cars and electronic devices to run longer on a single charge.
However, the solid materials inside these batteries expand and shrink as lithium ions move back and forth during operation. These changes can create tiny cracks and damage the contact between the battery’s components.
To keep everything connected, solid-state batteries are usually operated under high pressure. But this pressure has made it extremely difficult for scientists to observe what is happening inside the batteries while they work.
To solve this problem, Elmar Kataev developed a special experimental setup that allowed researchers to study the batteries in real operating conditions without destroying them.
The team used powerful X-ray techniques at the BESSY II research facility to examine both the battery surface and the hidden internal interfaces at the same time. By combining soft and hard X-ray photoelectron spectroscopy, the scientists could observe chemical reactions deep inside the battery while it was actively cycling.
The researchers studied a type of solid-state battery made with titanium sulfide and lithium yttrium chloride materials.
What they found was surprising.
During battery operation, oxygen-containing compounds inside the cell slowly moved toward the cathode current collector. Once there, the oxygen reacted with the active electrode material and formed a disordered layer rich in titanium oxides.
According to Katherine Mazzio, this unwanted layer is one of the main reasons the battery rapidly loses its ability to store energy.
The discovery points to oxygen contamination as a major hidden problem in solid-state batteries.
Scientists say the findings could help improve future battery designs by reducing or eliminating oxygen exposure during manufacturing. Producing battery materials in carefully controlled inert gas environments may help prevent these damaging reactions from occurring.
The study also demonstrates the importance of observing batteries while they are actually operating. Many degradation processes happen deep inside the cell and cannot be detected using traditional methods.
Researchers believe the new approach could help accelerate the development of longer-lasting solid-state batteries for electric vehicles, renewable energy storage, and portable electronics.
Although solid-state batteries still face technical challenges, the new findings provide scientists with a much clearer picture of why these promising batteries fail—and how they might eventually be made more reliable.
