Niwa Hideharu, Takachi Masamitsu, Okamoto Jun, Wu Wen-Bin, Chu Yen-Yi, Singh Amol, Huang Di-Jing, Moritomo Yutaka
Faculty of Pure and Applied Science, University of Tsukuba, Tsukuba, 305-8571, Japan.
Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba, 305-8571, Japan.
Sci Rep. 2017 Nov 29;7(1):16579. doi: 10.1038/s41598-017-16808-1.
Secondary batteries are important energy storage devices for a mobile equipment, an electric car, and a large-scale energy storage. Nevertheless, variation of the local electronic state of the battery materials in the charge (or oxidization) process are still unclear. Here, we investigated the local electronic state of cobalt-hexacyanoferrate (Na Co[Fe(CN)]), by means of resonant inelastic X-ray scattering (RIXS) with high energy resolution (~100 meV). The L-edge RIXS is one of the most powerful spectroscopic technique with element- and valence-selectivity. We found that the local electronic state around Co in the partially-charged NaCoCo[Fe(CN)] film (x = 1.1) is the same as that of the discharged NaCo[Fe(CN)] film (x = 1.6) within the energy resolution, indicating that the local electronic state around Co is invariant against the partial oxidization. In addition, the local electronic state around the oxidized Co is essentially the same as that of the fully-charged film Co[Fe(CN)][Fe(CN)] (x = 0.0) film. Such a strong localization of the oxidized Co state is advantageous for the reversibility of the redox process, since the localization reduces extra reaction within the materials and resultant deterioration.
二次电池是移动设备、电动汽车和大规模储能的重要储能装置。然而，电池材料在充电（或氧化）过程中局部电子态的变化仍不清楚。在此，我们通过具有高能量分辨率（约100 meV）的共振非弹性X射线散射（RIXS）研究了六氰合铁酸钴（Na Co[Fe(CN)]）的局部电子态。L边RIXS是最强大的具有元素和价态选择性的光谱技术之一。我们发现，在能量分辨率范围内，部分充电的NaCoCo[Fe(CN)]薄膜（x = 1.1）中Co周围的局部电子态与放电的NaCo[Fe(CN)]薄膜（x = 1.6）中的相同，这表明Co周围的局部电子态对部分氧化是不变的。此外，氧化Co周围的局部电子态与完全充电的薄膜Co[Fe(CN)][Fe(CN)]（x = 0.0）薄膜的基本相同。氧化Co态的这种强局域化有利于氧化还原过程的可逆性，因为局域化减少了材料内的额外反应和由此导致的劣化。
