P2-Type Na-0.Mn-67(0).Fe-65(0).Ni-20(0).O-15(2) Microspheres as a Positive Electrode Material with a Promising Electrochemical Performance for Na-Ion Batteries
Research activities on Na- ion battery materials have gained importance in recent years as Na- ion batteries are considered as an economical substitute for the Li-ion batteries in some future applications. In the present work, P2-type Na0.67Mn0.65Fe0.20Ni0.15O2 was synthesized in microspherical morphology and characterized. Microspheres of FeCO3 were first prepared and used to synthesize Mn0.65Fe0.20Ni0.15CO3, followed by its thermal decomposition to the corresponding oxide and finally the thermal fusion of the oxide with Na2CO3 to produce P2-type Na0.67Mn0.65Fe0.20Ni0.15O2. The sodiated mixedmetal oxide formed inmicrospherical morphology is in a pure crystalline phase with a mesoporous structure of average pore size 29 nm. Cyclic voltammograms of electrodes are characterized by well-defined two pairs of peaks corresponding to the oxidation and reduction processes in two different stages. The sodiated oxide provides an initial discharge capacity of about 216 mAh g-1 with an excellent cycling stability upon cycling at C/15 rate. The rate of decay in discharge 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 the porous microspherical morphology. (C) 2017 The Electrochemical Society. All rights reserved.