Switching Redox-Active Sites by Valence Tautomerism in Prussian Blue Analogues AxMny[Fe(CN)₆]·nH₂O (A: K, Rb): Robust Frameworks for Reversible Li Storage

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 A x Mn y [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.