Mechanical compression of electrolytes in solid-state batteries prevents short-circuits

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"In brief

• A SLAC/Stanford University research team found they could prevent short-circuiting of solid-state batteries by deflecting the dendrite propagation direction using mechanical compression.
• They provided direct evidence that dendrites start in the interior rather than merely at the surface of the electrolyte, settling a long-standing debate within the field.
• The results could have implications for future battery design by incorporating built-in mechanical compression or electrolytes with more defect-free interiors that suppress dendrite initiation.

...

Now, in a study ... researchers have discovered a way to both track these dendrites and suppress them enough to keep the battery from short-circuiting. ...

The team found that when they applied a metal ring to compress the solid electrolyte, it prevented vertical dendrites – the kind that cause short-circuiting – from forming during charging. ...

In fact, under this compression, batteries lasted for thousands of cycles. While vertical dendrites did not form, horizontal dendrites formed internally, but these did not reach the electrodes and therefore did not cause immediate short-circuiting. ...

Under compression, dendrites still formed during charging, but they spread horizontally instead of vertically. ..."

From the abstract:

"Lithium-metal solid-state batteries offer advantages of high energy density and improved safety compared with lithium-ion batteries.

However, solid-state batteries fail through short-circuiting even at low charging rates (less than 1 mA cm−2) due to lithium dendrite initiation and propagation.

The location of dendrite initiation is under debate, particularly regarding whether initiation occurs within the interior of the solid electrolyte or at the surface.

Here we develop an in-plane biaxial compression method that provides direct evidence that dendrite initiation occurs within the interior of garnet Li6.6La3Zr1.6Ta0.4O12 solid electrolytes during long-term cycling when the surface initiation mechanisms are rendered ineffective in shorting the cell.

The biaxial compression deflects dendrite propagation so that it is perpendicular to the electric field direction, leading to the generation of an unprecedentedly high density of dendrites without short-circuiting, even at an extreme fast-charging rate of 100 mA cm−2.

After long-term cycling, dendrites eventually appeared throughout the entire thickness of the solid electrolyte.

Under extreme cycling conditions, isolated lithium deposits are observed at grain-boundary junctions and pores, and these act as the dendrite initiation sites.

This work reconciles the surface and interior initiation mechanisms in garnet solid electrolytes and demonstrates that in-plane biaxial compressive stress can prevent both from short-circuiting the cell."

Squeezing solid-state batteries prevents short-circuits | Stanford Report "SLAC and Stanford research shows that mechanical compression stops lithium buildup in solid-state batteries, making them faster to charge and longer-lasting."

Dendrite initiation and deflection in biaxially stressed solid electrolytes (no public access)

Dendrite initiation and deflection in biaxially compressed solid electrolytes (preprint, open access)

Compressed electrolyte showing horizontal dendrite propagation, which prevents short-circuiting.