Solid-State Synthesis and Characterization of Mg-Substituted P2-Na_0.70Ni_0.45Mn_0.55O₂ Cathode Materials for Practical Sodium-Ion Batteries

Sodium ion batteries are considered as a potential alternative to existing Li-ion batteries. Layered transition metal oxides are found to be suitable cathode candidates for Na-ion batteries. In this study, solid state synthesis of P2-Na0.7Ni0.45Mn0.55O2 with different Mg substitutions is reported. The synthesized materials are characterized thoroughly using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and x-ray photoemission spectroscopy (XPS) analysis. SEM analysis reveals the morphology of synthesized materials to layered structure with a particle size in the range of 5-50 mu m. Powder XRD shows all synthesized materials of P2 structure irrespective of Mg substitution. A spurious P3 phase is observed in 0% and 5% of Mg substituted samples which are absent in 10% and 15% of Mg substituted materials. Electrochemical performance analysis shows specific capacity reduces with Mg substitution whereas mid-voltage reaches maximum up to 3.5 V with 10% substitution. 10% Mg substituted NMO shows a specific capacity 105 mA h g(-1) in the voltage ranges of 2-4.3 V versus Na/Na+ with excellent cycling stability and rate capability.