Abstract <p>It has been shown that a material based on sodium ferrate NaFeO₂ can be obtained by synthesis from a melt in a solar furnace. The crystal structure is tetragonal with the lattice parameters of <i>a</i> = 5.638 Å, <i>b</i> = 5.672 Å, and <i>c</i> = 7.279 Å. The average particle size of the material is 1.2 μm. It has been found that the NaFeO₂ material sample provides the oxidation–reduction activity of Na⁺/Na and the oxidation–reduction activity of Fe²⁺/Fe³⁺. Therefore, NaFeO₂ can be a potential material for the cathode of a sodium-ion battery with a specific capacity of 110 mAh/g. It has been found that sodium ferrate NaFeO₂ exhibits sufficiently good resistance to water. That is, sodium ferrate does not decompose in water at 80–100°C.</p>