Demonstrating the dual role of AlxOy coatings on LiNiO2 cathodes in pouch cells via operando and surface-sensitive X-ray techniques

Lithium nickel oxide (LNO) cathodes offer high capacity for high-energy-density applications but suffer rapid degradation above 4.2 V due to surface and bulk instabilities. Here, we apply an ultrathin aluminum oxide coating using powder atomic layer deposition to improve surface stability. Pouch cell testing shows that coated LNO delivers improved cycling behavior, retaining 91.2% capacity after 100 cycles at C/3. Operando X-ray diffraction reveals that after aging, coated LNO undergoes a less kinetically hindered delithiation, indicating that the surface coating further provides a surface-to-bulk stabilization effect. Postmortem surface sensitive spectroscopy confirms that the aluminum oxide layer (1) scavenges hydrofluoric acid and (2) suppresses surface reconstruction, reducing impedance growth and improving the surface integrity. Overall, the results demonstrate that ultrathin aluminum oxide coatings effectively mitigate interfacial degradation and enhance bulk electrochemical kinetics, providing an effective and scalable approach toward improving the long-term performance of ultra-Ni-rich cathodes.