Lattice Compensation to Jahn–Teller Distortion in Na-Rich Manganese Hexacyanoferrate for Li-Ion Storage: An Operando Study

Manganese hexacyanoferrate (MnHCF) has received increasing attention as a positive electrode for either lithium- or sodium-ion storage owing to its high specific capacity among the Prussian blue analogues (PBAs). During ion release, the material undergoes the Jahn–Teller distortion arising from the oxidation of manganese to its trivalent state. Typically, the Jahn–Teller distortion is reported to destabilize the host structure of electrode materials based on layered and spinel manganese oxides, resulting in volume changes in the order of 10–20%, which deteriorate the cycle performance. Herein, the effect of such a distortion on MnHCF via operando, synchrotron powder diffraction is reported. Surprisingly, only a minor volume change (about 2%) is recorded upon cycling the electrode material against lithium, highlighting the major role of the PBA framework in stabilizing the PBAs’ structures.