Periodic law-guided design of highly stable O3-type layered oxide cathodes for practical sodium-ion batteries†

Abstract

O3-type NaNi_0.5Mn_0.5O₂ cathode material exhibits significant potential for sodium-ion batteries (SIBs) owing to its high theoretical capacity and ample sodium reservoir. Nonetheless, its practical implementation encounters considerable obstacles, such as impaired structural integrity, sensitivity to moisture, inadequate high-temperature stability, and being unstable under high-voltage conditions. This study investigates the co-substitution of Cu, Mg, and Ti, guided by principles of the periodic law, to enhance the material's stability under varying conditions. The substituent elements were selected based on their atomic properties and introduced into specific sites within the structure: Cu and Mg were substituted at Ni sites, while Ti replaced Mn sites. These modifications strengthened the crystal lattice, mitigating phase transitions, and improved electrochemical performance. The O3-type NaNi_0.4Cu_0.05Mg_0.05Mn_0.3Ti_0.2O₂ material exhibited remarkable moisture stability, maintaining 85% of its capacity after 1000 cycles at 5C in 2.0–4.0 V. It also exhibited reversible phase transitions at voltages up to 4.3 V, with no oxygen release observed even when charged to 4.5 V. Furthermore, it exhibited remarkable high-temperature stability in half-cell testing and excellent cycling performance in full-cell evaluations. These results are very helpful for designing high-performance SIB cathodes that can withstand a variety of operating circumstances and ensuring structural stability.