Morphology Control of Al Oxide Coating to Suppress Interfacial Degradation in Ultra-high Nickel Cathode Materials

•The island-shaped Al coating (Al-400) was applied on ultra-high Ni cathode material through the controlling morphology.•The partially exposed surface of Al-400 suppressed impedance increase, achieving high capacity compared to fully covered coating.•Al-400 effectively reduced the electrolyte decomposition reaction and cross-talk to the anode surface.•Maintenance of the coating integrity from HF attack contributed to the enhanced long-term cycling stability of Al-400. Although ultra-high nickel layered cathode materials (LiNixCoyMn1−x−yO2, x ≥ 0.9, NCM90) offer advantages of high energy density and cost-effectiveness, the deterioration of cycle characteristics remains a challenge due to electrolyte decomposition reactions and irreversible phase transitions. In this study, we explored the morphology-controlled Al oxide coatings to mitigate cycle degradation in NCM90. The coating layer was applied in an island-shaped morphology, forming a relatively thick layer compared to fully passivated film-shaped coatings. This morphology effectively suppresses increasing impedance, reduces electrolyte decomposition reactions, and limits the dissolution of transition metals during the electrochemical cycling. It also provides high stability across both normal (3.0-4.3 V) and high (3.0-4.5 V) voltage ranges due to the maintenance of coating integrity against HF attacks. This study underscores the importance of a strategically engineered coating layer, demonstrating that an island-shaped morphology can significantly enhance the cycle performance of NCM90.