Effect of Coprecipitation Conditions on the Properties of FE_0.5MN_0.5CO₃ Sodium-Ion Cathode Precursors

Layered transition metal oxides are an attractive material for Na-ion batteries because of the possibility of using abundant and inexpensive materials such as Fe, Mn, and Na₂CO₃. However, scientific literature on the effect of coprecipitation parameters on Fe-containing cathode precursor materials is lacking. Herein, the effect of pH, temperature, and stirring rate on particle size distribution, tap density, surface area, and morphology of Fe_0.5Mn_0.5CO₃ precursors is studied. Higher coprecipitation temperature favors the formation of larger precursor particles. The highest tap densities between 1.8 and 1.9 g/cm³ were achieved at 60 °C. Particles with a usually preferred D50 of ≈10 μm were achieved when the precipitation temperature was around 40-50 °C. The particle size grew when the pH was increased, except at pH 8, where the smallest particles were achieved. The coprecipitation was not homogeneous, as the core of the particles was less dense than the outer layer of the particle and had a higher Fe concentration and a lower Mn and O concentration than the outer layer. High temperature and pH favored the formation of cubic or rhombohedral primary particles on the surface of the spherical particles. An even higher stirring rate (>1200 rpm) than what is possible with our experimental setup is preferred to prevent agglomeration. Further research should be done on the coprecipitation of Fe_1-<i>x</i> Mn _<i>x</i> CO₃ precursors.