Durable Cu-doped P3-Na0.62Mn1-xCuxO2 Cathodes for High-Capacity Sodium-ion Battery

Herein, this research presents a comprehensive study of the novel P3-Na0.62Mn1-xCuxO2 (x=0, 0.09, 0.19, and 0.28) material, elucidating the effects of partial Cu-doping on its structural and electrochemical characteristics. Our investigation employs operando X-ray diffraction (XRD), demonstrating a stable single-phase reaction during the battery's cycling operation accordingly preventing P3-O3 phase transition. Furthermore, operando differential electrochemical mass spectrometry (DEMS) demonstrates the absence of irreversible O2 evolution, hence affirming the stability of reversible oxygen redox processes in this material. Ex situ X-ray absorption near edge structure (XANES) study reveals substantial contributions from the Cu2+/Cu3+, Mn3+/Mn4+, and O2-/On- redox pairs to the overall capacity of the battery. The findings have been confirmed by X-ray photoelectron spectroscopy (XPS), which not only supports the results from the XANES investigation but significantly enhances them. Additionally, the oxygen redox processes have been established by the obvious widening apparent in the O K-edge XANES spectra and the detection of peroxo-like oxygen species in the XPS spectra when the battery is charged to 4.7 V. The electrochemical properties of P3-Na0.62Mn0.75Cu0.19O2 material have been extensively investigated, demonstrating high capacity (212.2 mAh g-1 at 20 mA g-1) and excellent rate performance due to the incorporation of electrochemically active Cu2+ ions. And finally, a full-cell of P3-Na0.62Mn0.75Cu0.19O2 with commercial hard carbon could achieve exceptional rate capability. This systematic approach highlights the key significance of Cu-doping for boosting electrochemical performance by promoting stable oxygen redox activities.