Surface engineering of Ni–Rich cathodes via Er2O3 coating for enhanced mechanical strength and reduced residual lithium species

Herein, we propose an Er-incorporated Ni-rich cathode material as an effective alternative for enhancing the structural stability of layered cathodes. Er, which has a strong binding affinity to oxygen, is incorporated at the Ni-rich cathodes to reinforce their mechanical hardness and suppress microcrack propagation during cycling. Mechanical analysis reveals that Er₂O₃ coating improves the hardness of LiNi_0.92Co_0.04Mn_0.04O₂ (NCM92), and the partial thermal reaction of Er₂O₃ with residual LiOH generates protective components, among which LiErO₂ decreases internal pressure and enhances rate capability by reducing LiOH content. During cycling, 2.0 wt% Er-modified NCM92 shows improved capacity retention compared to pristine NCM92. Severe particle cracking is observed in non-coated NCM92, while the Er-coated sample maintains intact secondary particle morphology, demonstrating the stress-relieving effect of Er-based coating. X-ray diffraction analysis reveals the collapse of the layered structure in cycled non-coated NCM92, whereas the Er-coated NCM92 retains a clear layered structure after 150 cycles.