From Failure to Design: Modulating Phase Transitions and Oxygen Release in Ni-Rich Cathodes

Ni-rich layered oxides (LiNi_xCo_yMn_zO₂, x + y + z = 1, x ≥ 0.8) are among the most promising cathode materials for high-energy-density lithium-ion batteries (LIBs); however, their structural instability during cycling significantly impedes large-scale commercialization. Conventional approaches have primarily aimed at suppressing phase transitions and oxygen vacancies (OVs), as these have long been regarded as detrimental owing to their close association with voltage decay, capacity fading, and interface degradation. In contrast, this review highlights a paradigm shift from conventional suppression strategies to the controlled utilization of these structural features. Specifically, localized spinel domains facilitate Li⁺ diffusion and act as stress buffers, whereas well-regulated oxygen vacancies enhance electrochemical kinetics and structural robustness. We critically examine the dual roles of these structural features and summarize advanced regulation strategies, including doping engineering, surface modification, and innovative synthesis methods, which collectively enable precise manipulation of phase transitions and defect chemistry. Furthermore, we emphasize the integration of in situ/operando characterization, multiscale computational modeling, and machine learning as indispensable tools for guiding the rational design of next-generation cathodes. Overall, this review establishes a comprehensive framework for transforming conventional failure mechanisms into proactive stabilization strategies, thereby addressing the long-standing trade-offs among energy density, cycle life, and safety in Ni-rich systems.