Understanding Reactivities of Ni-Rich Li[Ni_xMn_yCo_1–x–y]O₂ Single-Crystal Cathode Materials

While Ni-rich Li[NixMnyCo1–x–y]O2 (NMC, x ≥ 0.8) compounds are considered the most promising cathode materials for high-energy lithium-ion batteries (LIBs), a significant challenge is the higher reactivities caused by the increased Ni content, especially under high-voltage operation conditions. In the present study, we synthesize three single-crystal NMC (SC-NMC) samples with the same particle size and morphology: LiNi0.8Mn0.1Co0.1O2 (NMC811), LiNi0.80Mn0.15Co0.05O2 (NMC80155), and LiNi0.85Mn0.10Co0.05O2 (NMC85105). By systematically varying the composition while maintaining other properties, the role of each transition metal during air exposure, thermal treatment, and long-term cycling is clearly demonstrated. We reveal that while higher Ni content leads to overall increased reactivities, the presence of Mn provides a stabilizing effect on thermal, structural, and chemical properties. In the absence of cycling-induced particle cracking, surface reconstruction is shown to be the dominating contributor to cathode capacity fade. Our study provides key insights needed for the development of better-performing Ni-rich NMC cathode materials.