Moisture and Air-Stable Cation Disordered O3-Type Layered Cathode for Sodium-Ion Batteries: Experimental and First-Principles Study

Sodium-ion batteries have garnered unprecedented attention as a large-scale energy storage solution. However, the key challenges are to develop sustainable, low-cost, high-capacity, air and moisture-stable cathodes. In this context, we report an O3-type Na0.97 Ca0.03Ni0.4Cu0.1Mn0.3Al0.05Ti0.1Sb0.05O2 (NaMMeO), which delivers a reversible capacity of 132 mAh/g and a capacity retention of 81% after 100 cycles in the voltage range of 2.0-4.2V. Further, the cathode suppresses the intermediate phases and exhibits O3-P3 transitions underscoring its efficacy. The improved electrochemical performance of the NaMMeO is due to the disorder in the transition metal layer and also the diffusion of calcium into the sodium layer causing Na+/vacancy disordering. Moreover, the reduced Na interlayer spacing and the increased average redox voltage result in enhanced moisture and air stability. The mechanistic insights into the performance have been revealed through first-principles calculations. Computational observations complement the experimental data and provide a detailed atomic-level understanding of the electrochemical processes, such as reversible phase transitions, identifying the specific contributions of different elements in the redox process, and explaining the role of dopants in ameliorated moisture and air stability. This work provides valuable insights for developing an advanced O3-type layered oxide cathode materials for sodium-ion batteries.