Co-Free P2–Na_0.67Mn_0.6Fe_0.25Al_0.15O₂ as Promising Cathode Material for Sodium-Ion Batteries

P2–Na0.67Mn0.6Fe0.25Al0.15O2 (NaMFA) was developed as a cheaper and less-toxic cathode material for sodium-ion batteries than the Co analogous, P2–Na0.67Mn0.6Fe0.25Co0.15O2 (NaMFC). Despite cobalt being considered to stabilize layered structures upon cycling, NaMFA proved to have not only a higher specific charge 163 mAh g–1 compared to 141 mAh g–1 at a 0.1 C rate but also a better cycling stability and rate capability than NaMFC. The structural transitions occurring during sodiation/desodiation in the layered frames were characterized by operando X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) analyses. Aluminum was found to stabilize the P2-phase and favor the Mn reduction on discharge, increasing the amount of Na atoms reintercalated in the structure.