Primary-Particle Engineering Enables Durable O2/O3 Dual-Phase Li-Rich Cathodes

O2/O3 dual-phase Li-rich layered oxides are promising high-energy cathodes, but the microstructural factors governing their electrochemical durability remain unclear. Here, we demonstrate that primary-particle engineering is essential for realizing durable performance in O2/O3 dual-phase Li-rich cathodes. By varying the precursor calcination temperature from 700 to 900 °C, we regulate the primary-particle size while preserving the O2/O3 layered framework. The optimized sample prepared at 750 °C delivers an initial discharge capacity of approximately 260 mAh g-1 and retains 83.7% of its capacity after 100 cycles at 0.1 C. In contrast, particle coarsening at 900 °C limits low-voltage capacity utilization, accelerates voltage fade, and induces severe intergranular cracking. The optimized cathode also achieves 75.8% discharge-energy retention after 200 cycles at 0.5 C in a pouch-type full cell, 13% higher than that of a conventional O3-type Li-rich cathode. These findings establish primary-particle engineering as a critical design strategy for durable O2/O3 dual-phase Li-rich cathodes.