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.