The temperature (T) dependence of the sodium ion diffusion coefficient D of a NaxMnO2 thin film is extensively investigated versus x and T using electrochemical impedance spectroscopy. D is found to be 5.0 × 10-11cm2/s at x = 0.54 at 301 K, which is much larger than the value of 0.7 × 10-11cm2/s at x = 0.54 at 303K of a NaxCoO2 thin film. In addition, the activation energy Ea D of D (= 0.26-0.32 eV) is smaller than that of NaxCoO2 (= 0.31-0.44 eV). The improved Na+ diffusion properties of NaxMnO2 are interpreted in terms of the larger interlayer distance (d = 5.54 Å) of NaxMnO 2.
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