The Origin of High-Voltage Stability in Single-Crystal Layered Ni-Rich Cathode Materials.

Compared with the polycrystal (PC) Ni-rich cathode materials, the single-crystal (SC) counterpart displayed excellent structural stability, high reversible capacity and limited voltage decay during cycling, which received great attention from academics and industry. However, the origin of fascinating high-voltage stability within SC is poorly understood yet. Herein, we tracked the evolution of phase transitions, in which the destructive volume change and H3 phase formation presented in PC, are effectively suppressed in SC when cycling at a high cut-off voltage of 4.6 V, further clarifying the origin of high-voltage stability in SC cathode. Moreover, SC electrode displayed crack-free morphology, and excellent electrochemical stability during long-term cycling, whereas PC suffered severe capacity and voltage fade because of the spinel-like phase, decoding the failure mechanisms of PC and SC during cycling at high cut-off voltages. This finding provides universal insights into high-voltage stability and failure mechanisms of layered Ni-rich cathode materials.