Revealing the Role of Ruthenium on the Performance of P2-Type Na_0.67Mn_1-xRu_xO₂ Cathodes for Na-Ion Full-Cells

Herein, P2-type layered manganese and ruthenium oxide is synthesized as an outstanding intercalation cathode material for high-energy density Na-ion batteries (NIBs). P2-type sodium deficient transition metal oxide structure, Na_0.67Mn_1-xRu_xO₂ cathodes where x varied between 0.05 and 0.5 are fabricated. The partially substituted main phase where x = 0.4 exhibits the best electrochemical performance with a discharge capacity of ≈170 mAh g^-1. The in situ X-ray Absorption Spectroscopy (XAS) and time-resolved X-ray Diffraction (TR-XRD) measurements are performed to elucidate the neighborhood of the local structure and lattice parameters during cycling. X-ray photoelectron spectroscopy (XPS) revealed the oxygen-rich structure when Ru is introduced. Density of States (DOS) calculations revealed the Fermi-Level bandgap increases when Ru is doped, which enhances the electronic conductivity of the cathode. Furthermore, magnetization calculations revealed the presence of stronger Ru─O bonds and the stabilizing effect of Ru-doping on MnO6 octahedra. The results of Time-of-flight secondary-ion mass spectroscopy (TOF-SIMS) revealed that the Ru-doped sample has more sodium and oxygenated-based species on the surface, while the inner layers mainly contain Ru-O and Mn-O species. The full cell study demonstrated the outstanding capacity retention where the cell maintained 70% of its initial capacity at 1 C-rate after 500 cycles.