Self-Consistent DFT+ <i>U</i> Insight into Electronic Properties, Intercalation Voltages, and Sodium Migration Mechanisms of Manganite Na-Ion Cathode Materials

Optimizing the electrochemical performance of sodium manganites as high-energy cathode materials for sodium-ion batteries requires a deep understanding of their electronic properties, intercalation voltages and sodium migration mechanisms. In this work, we present a comprehensive study of pristine (NaxMnO2), doped (NaxLi0.17Mg0.17Mn0.66O2) and mixed transition-metal (NaxNi0.33Mn0.67O2, NaxTi0.17Ni0.33Mn0.5O2, and NaxFe0.17Ni0.33Mn0.5O2) P2-type layered sodium manganese oxides (x = 0 and x = 1), based on density functional theory with on-site U Hubbard interactions to accurately model the properties arising from the strongly correlated nature of transition-metal 3d states in these lamellar systems. The on-site U Hubbard parameters are computed fully from first-principles using linear response theory. For these mixed-valence cathodic materials, we report calculated oxidation states and intercalation voltages in very good agreement with experimental measurements. Moreover, sodium migration pathways are studied, elucidating the activation energies, the migration mechanisms and their tuning with substitution. In particular, Ni and Ti substitution emerges as the most promising strategy for realizing a fully post-lithium and high-performance cathode. Our findings advance the rational design of next-generation energy storage materials by combining advanced computational techniques with experimental validation, offering insights into optimizing the electrochemical and ionic transport properties of sodium-based positive electrodes.