Sodium-ion batteries have been prospective substitutes for lithium-ion systems in large-scale energy storage because of the abundance and low price of sodium. This dissertation documents the synthesis and characterization of layered Naₓ(Ni₀.₁₃Mn₀.₅₄Co₀.₁₃)O₂ (Na-NMC) cathodes with different sodium compositions. Na-NMC precursors were synthesized through the hydrothermal method to prepare NMC carbonate compounds, which were then sodiated via solid-state sodiation at 850 °C using Na₂CO₃ to obtain the final layered oxides. Phase and structural X-ray diffraction analysis established formation of a hexagonal P2-type layered structure in all materials. Scanning electron microscopy indicated varied particle morphology and size with sodium concentration, with greater-Na samples demonstrating more distinct plate-like particles. Near-stoichiometric transition metal ratios and successful sodium incorporation into the oxide structure were confirmed by energy-dispersive X-ray spectroscopy and ICP-OES. Electrochemical characterization in coin cells showed that elevated Na content tended to enhance the reversible capacity, corresponding to more initial Na occupancy. The best samples for sodium loading, however, exhibited capacity variation and low coulombic efficiency due to possible residual sodium phases or side reactions. These results suggest that sodium content can be optimized to increase energy capacity but highlight the importance of controlling unwanted phases at high sodium levels. The work highlights that although increasing the sodium content increases capacity, too much sodium can bring with it stability problems, so stoichiometry needs to be carefully balanced. This research supplies valuable information on the way sodium stoichiometry affects the structure and electrochemical properties of layered oxide cathodes. These results justify the ongoing research and development of high-performance, sustainable cathode materials for sodium-ion batteries.
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