Reconciling the O3-P3 phase transition in layered oxides to reduce particle strain for stable sodium battery cycling

O3-type layered positive electrode materials for sodium-ion batteries exhibit high specific energy but suffer from phase transitions during charge-discharge cycling, which generate significant lattice strain and compromise structural integrity. Using a model high-entropy positive electrode (Na0.83Fe0.22Ni0.18Cu0.05Co0.05Zn0.075Li0.025Mn0.275Ti0.05Sb0.05Mg0.025O2), here we show, these phase transitions are conventionally kinetics-limited, occurring at states far removed from thermodynamic stability. By tailoring configurational entropy to regulate diffusion kinetics, we can delay the onset of phase transitions from kinetic barriers to thermodynamic stability, yielding an O3-type positive electrode with enhanced phase stability. Multiscale spatial resolution diffraction analysis reveals a reduction in internal stress due to suppressed kinetically driven early phase transitions. This advanced material achieves a high specific energy of 162.5 Wh/kg at the full‑cell total weight level at 0.1 C, retains 97.7% capacity at 5 C/1 C (650/130 mA/g), and maintains 90% capacity retention after 2300 cycles in Ah-level pouch cells, positioning it as a promising candidate for practical applications. The utilization of thermodynamically driven phase transition provides a promising alternative direction for preparing high performance layered sodium positive electrodes. O3-type layered cathodes offer high energy density for sodium-ion batteries, but phase transitions can undermine their stability. Here, authors show that tailoring configurational entropy regulates diffusion kinetics and delays phase transitions, enabling a high-energy cathode with long cycle life and improved structural integrity.