Understanding the Mechanistic Pathways of Layered Oxide Cathode Synthesis for Sodium-Ion Batteries

Abstract

Sodium-ion batteries (SIBs) offer cost-effective and earth-abundant complementary technology to lithium-based systems, positioning them as promising candidates for large-scale energy storage to meet the world's exponentially growing energy demands. This dissertation investigates the interconnected roles of precursor chemistry, interfacial solid-liquid interactions, and calcination pathways involved in the synthesis of Ni-Fe-Mn –based layered oxide cathodes for sodium-ion batteries. It begins by examining equimolar Ni-Fe-Mn hydroxide precursors synthesized byammonia- and citrate-based co-precipitation routes, comparing their morphological control, stoichiometric accuracy, and structural homogeneity under varying reaction conditions. Motivated by the challenges observed in synthesis, the second study shifts focus to a fundamental investigation of metal–ligand interactions at the solid–liquid interface. Using in-situ synchrotron X-ray fluorescence microscopy and statistical modeling, we quantify how pH and metal identity influence interfacial dissolution-redeposition dynamics of multiple transition metals in alkaline media and reveal metal-specific spatial–temporal trends within multicomponent systems.Subsequent chapters shift focus to the high-temperature solid-state transformation of these precursors into NaNi1/3Fe1/3Mn1/3O2 cathodes. First, we analyze the mechanistic reaction pathway of sodium carbonate-based calcination, identifying key stages of precursor dehydration, major intermediate formation, and grain growth behavior. We then systematically investigate how variations in precursor design route and sodium source influence calcination behavior, demonstrating that structural and morphological differences govern distinct phase evolution pathways, ranging from topotactic transformations to complex multistep transformation. Finally, we extend this methodology to Mn-rich systems for P2-type sodium layered oxides, demonstrating that citrate-based strategies can yield favorable particle morphologies across a range of manganese-rich compositions, despite challenges associated with Mn precipitation. Across these studies, we establish a framework for linking precursor synthesis to downstream calcination outcomes, offering new insights into optimizing reaction parameters for more efficient synthesis of sodium-ion layered oxide cathodes.