Na‐site energy of P2‐type NaxM O2 (M = Mn and Co) |
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| Authors: | D Tanabe T Shimono W Kobayashi Y Moritomo |
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| Institution: | 1. Graduate School of Pure and Applied Sciences, University of Tsukuba, Ibaraki 305‐8571, Japan;2. Tsukuba Research Center for Interdisciplinary Materials Science (TIMS), University of Tsukuba, Ibaraki 305‐8571, Japan |
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| Abstract: | P2‐type NaxM O2 (M = Mn and Co) is a promising cathode material for low‐cost sodium ion secondary batteries. In this structure, there are two different crystallographic Nai (i = 1 and 2) sites with different Coulomb potential $ (\varphi _i)$ provided by M4–x and O2–. Here, we experimentally determine a difference ${(\rm \Delta }\varepsilon \equiv \varepsilon _1 - \varepsilon _2)$ of Na‐site energies ${(}\varepsilon _i \equiv e\varphi {\kern 1pt} _i)$ based on the temperature dependence of the site occupancies. We find that ${\rm \Delta }\varepsilon {=}56{K}$ for Na0.52MnO2 is significantly smaller than 190 K for Na0.59CoO2. We interpret the suppressed ${\rm \Delta }\varepsilon $ in Na0.52MnO2 in terms of the screening effect of the Na+ charge. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) |
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| Keywords: | Nax MnO2 Nax CoO2 X‐ray diffraction sodium ion secondary batteries crystal structure |
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