Abstract: To investigate the impact of ammonium sulfate concentration on the growth of manganese grains, this study was conducted under controlled conditions with a constant Mn²⁺ concentration of 20 g/L, Mg²⁺ concentration of 20 g/L, and current density of 450 A/m². By varying the electrodeposition duration, the effect of (NH₄)₂SO₄ concentration on the morphology and growth kinetics of electrodeposited manganese grains was examined. The results indicate that the growth of metallic manganese follows the screw dislocation mechanism, resulting in cauliflower-like grain structures. Regardless of the (NH₄)₂SO₄ concentration, all electrodeposited manganese exhibited an α-Mn crystal structure with a preferred orientation at the (411) plane. As the (NH₄)₂SO₄ concentration increased from 80 g/L to 120 g/L, the growth rate of manganese grains initially decreased and then increases. At lower concentrations of (NH₄)₂SO₄, grain growth was non-uniform, with some grains exhibiting preferential growth, while higher concentrations promoted uniform grain development. An optimal (NH₄)₂SO₄ concentration of 110 g/L yielded high current efficiency, along with lower cell voltage, and reduced energy consumption, making it the most favorable condition for economic performance.