Preparation and Characterisation of Battery-grade Na₂Mn₃O₇ as a Cathode Material from Manganese Ore

Natural battery-grade manganese dioxide with 69.78 mass% MnO₂ and 14.50% MnCO₃ was subjected to solid-state treatment to prepare a hybrid system with β-MnO₂ and Na₂Mn₃O₇ phases. The heat treatment was carried out at 400°C using NaOH/MnO₂ molar ratios ranging 0.4 to 1.2 and NaNO₃/MnO₂ molar ratios ranging 0 to 0.8. The structures of the samples were analysed using X-ray diffraction and differential scanning calorimetry. The electrochemical properties were evaluated through cyclic voltammetry, and the specific capacitance (C_S) values were calculated. The XRD results confirmed the formation of Na₂Mn₃O₇. The highest C_S (34.21 F g^-1) was obtained in the sample with 24.15 mass% Na₂Mn₃O₇. A thermodynamic analysis was also carried out to estimate the effect of the NaOH and NaNO₃ contents and of the temperature on the formation of Mn-based species.