Solid-state batteries are widely seen as the next big step in battery technology.
They could be safer, store more energy and help electric vehicles drive farther on a single charge.
However, scientists still need to solve several problems before these batteries become common.
Now, a new study has given researchers an important look inside a working solid-state battery, revealing how lithium moves during charging and why this movement is not always even.
The study, published in Advanced Energy Materials, was carried out by researchers from the Institut Laue-Langevin (ILL) and their partners.
Using a powerful technique called neutron diffraction, they were able to observe lithium moving inside a working solid-state battery in real time.
This is the first time scientists have watched this process so clearly inside a thick battery while it was operating.
Rechargeable lithium-ion batteries power many everyday devices, including smartphones, laptops and electric cars.
Most of these batteries contain a liquid electrolyte, which helps lithium ions move between the battery’s two electrodes during charging and discharging. While this design works well, the liquid can increase the risk of overheating or fire and limits how much battery performance can improve.
Solid-state batteries replace the liquid with a solid material. This could make batteries safer, smaller and able to store more energy.
But moving lithium through solid materials is much harder than moving it through a liquid. If lithium does not spread evenly, some parts of the battery charge faster than others, reducing efficiency and shortening battery life.
Looking inside a working battery is extremely difficult because it is sealed and made of thick layers of material. Lithium is also one of the lightest elements, making it hard to detect with many common scientific tools.
To overcome this problem, the researchers used neutron diffraction. Unlike X-rays, neutrons interact directly with atomic nuclei, making them especially sensitive to lithium. Neutrons can also travel deep into the battery without damaging it, allowing scientists to study what is happening throughout the entire battery while it is charging and discharging.
The team built a special solid-state battery for the experiment using advanced materials, including a newly developed solid electrolyte with much higher lithium conductivity than earlier versions. This improved material allowed the thick battery to perform well enough for detailed measurements.
As the battery charged, the researchers made an unexpected discovery. Instead of lithium leaving the battery material evenly, different parts of the positive electrode reached different charge levels at the same time. Even though the battery was charging very slowly, lithium movement was still uneven inside the thick electrode.
When the researchers repeated the experiment at a much higher temperature, the lithium spread much more evenly throughout the battery. The higher temperature allowed lithium ions to move more easily through the solid material, improving the charging process.
The study also brought good news. The solid electrolyte remained stable throughout the entire charging and discharging cycle, showing no signs of structural damage.
The researchers believe these findings will help engineers design better solid-state batteries in the future.
By understanding exactly how lithium moves inside a working battery, scientists can improve battery materials and designs, bringing safer, longer-lasting and more powerful batteries closer to everyday use.
