Researchers have identified a critical mechanism behind the failure of solid-state batteries, offering new clues that could help develop safer, longer-lasting energy storage technologies.
Every time a smartphone is charged or an electric vehicle is plugged in, billions of lithium ions move through a battery to store energy.
Not futuredevices can have much higher performance thanks to solid state batterieso, a technology that promises cell phones with greater autonomy, safer energy storage systems and electric vehicles capable of traveling much longer distances on a single charge.
But there is a persistent problem that has prevented these batteries from reaching widespread use: small structures called , which are capable of destroy a battery from the inside.
Now, researchers at the Max Planck Institute for Sustainable Materials (MPI-SusMat) have discovered exactly how these microscopic defects trigger battery failure. The findings, in Nature, offer a new perspective on one of the key challenges of next-generation energy storage.
Unlike conventional lithium-ion batteries, which rely on a liquid electrolyte to transport ions between electrodes, solid-state batteries use a solid ceramic electrolyte.
A Eliminating the liquid component brings several advantages. These systems can, in principle, store more energy in the same space, reduce the risk of fire and remain functional for longer, explains .
The technology has attracted enormous interest from automakers and electronics manufacturers because it could significantly improve battery performance.
In theory, smartphones could run for several days without being charged, while electric vehicles could achieve autonomy up to three times greater than current models.
How can soft lithium break hard ceramic?
Despite these advantages, solid-state batteries have a fragility surprising. During charging, needle-shaped dendrites can grow from the lithium anode and advance through the solid electrolyte.
If they reach the opposite electrode, create an internal short circuit which can quickly render the battery unusable.
What intrigued scientists was understand how lithium, a soft metal, could penetrate and fracture a much harder ceramic material and rigid.
P. Mehta / Max Planck Institute for Sustainable Materials
Comparison of the inside of a lithium-ion battery with that of a solid-state battery
“Although the electrodes and dendrites in formation are made of metallic lithium, which is soft like a jelly bear, the dendrites are able to penetrate the ceramic electrolyte and cause a short circuit,” he explained. Yuwei Zhanglead author of the study.
“How can soft dendrites fracture a solid, rigid ceramic? There are two hypotheses: or there is an accumulation of internal tensions inside the dendrites, which causes mechanical fracture of the solid electrolyte; or the electrons escape along the grain boundaries of the solid electrolyte, promoting the formation of lithium nuclei that eventually interconnect.”
To determine which explanation was correct, the researchers created a comprehensive experimental approach that allowed them to study materials in a vacuum and at cryogenic temperatures. These conditions prevented oxygen and moisture contamination and reduced unwanted effects associated with electron microscopy.
Battery failure mechanism revealed
The team took a closer look at lithium dendrites trapped in cracks in the ceramic electrolyte. The measurements did not reveal signs of lithium accumulation ahead of the advancing dendrite tip, a result that weakens the second hypothesis.
Instead, the results point to a pressure build-up within the dendrite itself. “The soft lithium metal can penetrate the hard ceramic electrolyte like a continuous jet of water passing through a rock. We calculate that the hydrostatic stress in the dendrite ultimately leads to brittle fracture of the solid electrolyte,” said Zhang.
With a clearer understanding of how dendrite-associated cracking occurs, the team is now studying ways to prevent.
Possible solutions include making the solid electrolyte more resistant to fracture, adding microscopic voids that deflect dendrite growth and reduce crack propagation, and applying protective coatings to lithium electrodes to limit dendrite formation.
According to the researchers, the work shows the importance of understanding, at a fundamental level, the behavior of materials when developing technologies aimed at real applications.
