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Scientists Found Out What Kills Solid-State Batteries and Are Working on a Solution

Solid-state batteries offer many advantages over their counterparts that use liquid electrolytes. They are inherently safe, thanks to the fact that the electrolyte is not flammable, and they can store more energy. Nevertheless, they are prone to dendrite formation, which shortens their life cycles. Scientists have discovered what causes the dendrites to penetrate the solid electrolyte and are working on a solution to prevent the problem.
Scientists found out what kills solid-state batteries 6 photos
Photo: MIT
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While Li-Ion batteries have been around for years, one of their most hyped variants is still in development. Replacing the liquid electrolyte with a solid one brings many advantages, the most important being safety. Solid-state batteries are also said to be lighter and hold more energy than liquid-electrolyte batteries in widespread use today. Nevertheless, solid-state batteries remain a scientist’s dream for now because they suffer from a mysterious problem that kills them prematurely. This makes them unsuitable for mass production, despite their advantages.

All lithium-ion batteries suffer from dendrite formation, but this happens very quickly in solid-state batteries. Dendrites are branch-like formations that can spread between batteries’ electrodes, causing them to short-circuit. Until now, it was a mystery how soft lithium dendrites could penetrate through the hard layer of the solid electrolyte. Thanks to scientists’ work, we know that nano-scale cracks developing in the solid electrolyte allow the dendrites to cross from one electrode to the other.

Stanford University and SLAC National Accelerator Laboratory researchers discovered what’s causing the problem. According to a study published on January 30 in the journal Nature Energy, the issue is caused by mechanical stress. This is interesting because the scientific world believed it was mainly a chemical problem. Finding the real cause means scientists can now focus on a solution so that the solid-state batteries can be all they promised.

“Just modest indentation, bending or twisting of the batteries can cause nanoscopic fissures in the materials to open and lithium to intrude into the solid electrolyte causing it to short circuit,” explained senior author William Chueh. “Even dust or other impurities introduced in manufacturing can generate enough stress to cause failure.”

The problem comes down to the fact that many leading solid electrolytes are ceramic. They offer the advantage of fast transport of lithium ions. Nevertheless, like all ceramic materials, they can develop tiny cracks on their surface, many less than 20 nanometers wide. These cracks can open during charging, allowing lithium to intrude. The researchers conducted more than 60 experiments to demonstrate their theory, each involving a miniature solid-state battery.

They found that the pressure exerted on the solid electrolyte affects the dendrite formation. More specifically, mechanical stresses like bending and twisting increase the probability that the battery short-circuits. Even a subtle bend or speck of dust caught between the electrolyte and the lithium anode will cause imperceptible crevices.

“Given the opportunity to burrow into the electrolyte, the lithium will eventually snake its way through, connecting the cathode and anode,” said Geoff McConohy, co-lead author of the study. “When that happens, the battery fails.”

Now that they explained what’s causing solid-state batteries to fail, Chueh’s team intends to use the knowledge to toughen the materials used as solid electrolytes. They are also looking at ways to cover the electrolyte’s surface with a coating to prevent cracks or repair them when they emerge. The study reminds us of a similar one signed by a team at MIT. In that case, the scientists found a way to control the direction of the dendrites by applying controlled mechanical stress on the electrolyte.
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About the author: Cristian Agatie
Cristian Agatie profile photo

After his childhood dream of becoming a "tractor operator" didn't pan out, Cristian turned to journalism, first in print and later moving to online media. His top interests are electric vehicles and new energy solutions.
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