August
Picture of the Month - August 2026
Impedance Growth in Ni-Rich Cathodes: Surface Reconstruction vs. CEI Evolution
Lithium-ion batteries store more energy per kilogram than any other practical chemistry, which is why they are used in electric vehicles and consumer electronics. Nickel-rich layered oxides (NCM) offer the highest specific capacities of the available cathode materials, but the more nickel they contain, the faster they degrade.
The primary driver of this degradation has long been debated: is it the surface film formed by electrolyte degradation (CEI), or the collapse of the underlying crystal structure (SRL)? Or both?
By combining impedance spectroscopy with advanced characterization (TEM, XPS, and SIMS), we separated the influence of these two mechanisms.
What we found:
· Crystal collapse, not CEI evolution, drives aging: The surface reconstruction layer (SRL) governs resistance growth and capacity loss. Over long high-voltage holds, the surface film thins while internal resistance continues to rise.
· Non-uniform degradation: The crystal structure collapses unevenly. As lithium is forced through the remaining intact pathways, current constriction causes a non-linear rise in resistance.
Each segment of the picture represents a different aging protocol, arranged clockwise by increasing stress. The particle is colored by structure, blue for layered, red for rock salt, and its shell by CEI chemistry, from organic-rich (teal) to inorganic-rich (green). As stress increases, the red rim expands inward while the shell thins, illustrating how current constriction drives resistance growth.
Publications:
Schröder, Vettori et al., Energy Storage Materials 2026, 88, 105115 https://doi.org/10.1016/j.ensm.2026.105115
Vettori, Schröder et al., Adv. Energy Mater. 2025, 15, 2502148 https://doi.org/10.1002/aenm.202502148
This picture was submitted by Steffen Schröder (group of Prof. Henss).
Further insights into the research activities of the ZfM groups can be found in the Gallery.