Altering the transition metal stoichiometry fundamentally changes the electrochemical behavior of the final sodiated cathode: (1) Nickel (Ni}^{2+} Enrichment (40%): Increasing nickel content expands the initial capacity of the material. The Ni^{2+}/Ni^{4+} redox couple acts as a primary multi-electron donor during sodium deintercalation/intercalation. (2) Iron (Fe^{3+)) Reduction (20%): Lowering the iron ratio to 20% mitigates the structural distortion and rapid capacity decay associated with the collective Jahn-Teller effect of high-spin Mn^{3+} formed through charge transfer with iron, while still keeping material costs low. (3) Manganese (Mn^{4+}) Stabilization (40%): A higher manganese fraction stays predominantly in the Mn^{4+} state, providing a robust structural scaffold that prevents phase transition collapse (such as the irreversible O3 to P3 phase shift) at high voltages.

The conversion of the precursor to the final active cathode active material occurs via high-temperature calcination with a sodium salt (typically sodium carbonate, Na2CO3, or sodium hydroxide, NaOH:

O3 vs. P2 Control: Sintering this exact precursor ratio around 800°C typically yields an O3-type phase, which maximizes initial specific capacity (~ 135 mAh/g} between 2.0–4.0V vs. Na/Na+). Atmospheric Sensitivity of Precursor: Unlike stable NMC precursors, NFM424 hydroxide powder is highly prone to moisture pickup and localized surface oxidation if left exposed to ambient air. It should be transferred and stored under vacuum or an inert gas blanket prior to calcination to ensure reproducible electrochemical properties.