Efficient Method of Designing Stable Layered Cathode Material for Sodium Ion Batteries Using Aluminum Doping

Despite their high specific capacity, sodium layered oxides suffer from severe capacity fading when cycled at higher voltages. This key issue must be addressed in order to develop high-performance cathodes for sodium ion batteries (SIBs). Herein, we present a comprehensive study on the influence of Al doping of Mn sites on the structural and electrochemical properties of a P2–Na0.5Mn0.5–xAlxCo0.5O2 (x = 0, 0.02, or 0.05) cathode for SIBs. Detailed structural, morphological, and electrochemical investigations were carried out using X-ray diffraction, cyclic voltammetry, and galvanostatic charge–discharge measurements, and some new insights are proposed. Rietveld refinement confirmed that Al doping caused TMO6 octahedra (TM = transition metal) shrinkage, resulting in wider interlayer spacing. After optimizing the aluminum concentration, the cathode exhibited remarkable electrochemical performance, with better stability and improved rate performance. Electrochemical impedance spectroscopy (EIS) measurements were performed at various states of charge to probe the surface and bulk effects of Al doping. The material presented here exhibits exceptional stability over 100 cycles within a 1.5–4.3 V window and outperforms several other Mn–Co-based cathodes for SIBs. This study presents a facile method for designing structurally stable cathodes for SIBs.