We report the structural and electrochemical properties of P2-type Na 0.67 Mn 1-x Cu x O 2 (where x=0.20 - 0.50) via various techniques. X-ray diffraction (XRD) reveals a reduction of the unit cell volume upon substitution of Cu elucidated through detailed Rietveld analysis. The cyclic voltammetry (CV) behaviors are also affected by the Cu substitution indicating new redox reactions stemming from Cu presence. Galvanostatic cycling measurements at room temperature show that when x=0.35 in P2-type Na 0.67 Mn 1-x Cu x O 2 cathode, the best electrochemical performance is obtained. Na-ion diffusion rate is found to be strongly dependent upon the environmental temperature. Changes in the valence state and the local structures of P2-type Na 0.67 Mn 1-x Cu x O 2 during the charge/discharge are elucidated through the Operando X-ray absorption spectroscopy (XAS) technique.
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