Voltage-dependent progression of failure mechanisms in single-crystal Ni-rich cathodes

The structural evolution and failure behavior of single-crystal LiNi_0.83Co_0.11Mn_0.06O₂ (NCM83) cathodes are systematically investigated under different upper cutoff voltages, revealing a clear voltage-dependent transition in failure mechanism. At a moderate cutoff voltage of 4.3 V, structural changes are confined primarily to a surface O3–O1 phase transition, accompanied by limited lattice distortion. Increasing the cutoff voltage to 4.4 V and 4.6 V triggers pronounced surface reconstruction, characterized by the progressive formation of spinel (LiNi₂O₄, Ni₃O₄) and rock-salt (NiO) phases, resulting in a thick electrochemically inactive surface layer. These irreversible phase transformations significantly impede Li⁺ transport. The development of internal cracking is found to be strongly correlated with the severity of phase transitions. High cutoff voltages induce large anisotropic volume changes and crystallographic incompatibility, leading to substantial internal stress accumulation and promoting intragranular microcrack formation. In situ stress measurements combined with scanning electron microscopy indicate suppressed plastic deformation and increased fracture susceptibility following high-voltage cycling. Collectively, increasing the cutoff voltage drives a transition in the dominant failure mechanism from bulk degradation governed by repeated Li⁺ insertion/extraction to surface phase breakdown coupled with mechanical damage, providing mechanistic insight into voltage window design and surface stabilization strategies for Ni-rich cathodes.