The discovery of a new electrode material that provides a reversible Li ion insertion/extraction reaction is of primary importance for Li ion batteries. In this report, electrochemical Li ion insertion/extraction in valence tautomeric Prussian blue analogues AxMny[Fe(CN)6] (A: K, Rb) was investigated. Ex situ X-ray diffraction experiments revealed that the K salt without the valence tautomerism exhibits the Li ion insertion/extraction with a redox process of an Fe ion, while the Rb salt with the valence tautomerism exhibits that with a redox process of a Mn ion. Regardless of the redox-active metal ions, highly reversible Li ion storage was achieved. The electronic structure changes during the Li ion insertion/extraction are confirmed by XPS experiments.
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