First realistic portraits of squishy layer that’s key to battery performance

Credit: Zewen Zhang/Stanford University

In next-gen lithium-metal batteries, the liquid between the electrodes, called the electrolyte, corrodes the surfaces of electrodes, forming a thin, squishy layer called SEI. To make atomic-scale images of this layer in its native environment, researchers inserted a metal grid into a working coin cell battery (left). When they removed it, thin films of electrolyte clung to tiny circular holes within the grid, held in place by surface tension, and SEI layers had formed on tiny lithium wires in those same holes. Researchers blotted away excess liquid (center) before plunging the grid into liquid nitrogen (right) to freeze the films into a glassy state for examination with cryo-EM. This yielded the first detailed images of the SEI layer in its natural swollen state.

« First realistic portraits of squishy layer that’s key to battery performance

Credit: Weijiang Zhou/Stanford University

Cryo-EM images of electrolyte clinging to holes in a sample grid show why it’s important to blot away excess electrolyte before freezing and imaging the samples. At top, excess electrolyte has frozen into a thick layer (right) and sometimes even formed crystals (left), blocking the microscope’s view of the tiny circular samples beneath. After blotting (bottom), the grid (left) and its tiny holes (right) can clearly be seen and probed with beams of electrons. SLAC and Stanford researchers used this method to make the first realistic cryo-EM images of a layer called SEI that forms on the surfaces of electrodes due to chemical reactions with the battery electrolyte.

« First realistic portraits of squishy layer that’s key to battery performance

Credit: Zewen Zhang/Stanford University

This video shows a lithium metal wire coated with a layer called SEI and saturated with the surrounding liquid electrolyte; the dashed lines represent the outer edges of this SEI layer. As the electrolyte is removed, the SEI dries out and shrinks (arrows) to about half its previous thickness. SLAC and Stanford researchers used cryo-EM to make the first clear, detailed images of the SEI layer in the wet environment of a working battery. The results suggest new ways to improve the performance of next-gen batteries.

« First realistic portraits of squishy layer that’s key to battery performance

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