Microspheres of P2-type Na_0.67Mn_0.65Fe_0.20Ni_0.15O₂as Cathode Material with Enhanced Na-ion Battery Performance

Research activities on Na-ion battery materials have gained importance in recent years as this battery is considered as an economical substitute for the Li-ion batteries in future. Sodium manganese oxide is reported as a high capacity positive electrode material of Na-ion battery. In the present work, P2-type Na_0.67Mn_0.65Fe_0.20Ni_0.15O₂ is synthesized in microspherical morphology and characterized for physicochemical and electrochemical properties. Microspheres of FeCO₃ are first prepared and used as the template to synthesize Mn_0.65Fe_0.20Ni_0.15CO₃, followed by its thermal decomposition to the corresponding oxide and finally the thermal fusion of the oxide and Na₂CO₃. The desired sodiated mixed metal oxide formed in microspherical morphology is pure crystalline phase with a wide mesopore size distributed at 29 nm. Cyclic voltammograms are characterized by well-defined two pairs of current peaks corresponding to the oxidation and reduction processes in two different stages. The sodiated oxide provides an initial discharge capacity of about 220 mAh g^-1 at C/15 rate cycling with an excellent stability. The rate of decay in discharged capacity is about 0.3 % per cycle at C/15 rate, but it increases to 0.9 % per cycle over 100 continuous charge-discharge cycles at higher rates. The rate capability is also high and the discharge capacity is about 100 mAh g^-1 at 2C rate. The high discharge capacity and high rate capability are attributed to porous microspherical morphology.

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