Structure of Fe-based Li/Na hybrid Prussian Blue Analogues

Prussian Blue Analogues (PBAs, AxM[M'(CN)6)]·zH2O) are a promising class of materials for sustainable positive battery electrodes, especially Prussian White (Na2-xFe[Fe(CN)6]) due to its high theoretical capacity (160-170 mAh/g) and high operating potential (~3.2 V). However, the material shows significant capacity fading due to the volume collapse of the framework during electrochemical cycling. It has been proposed that this can be resolved by the removal of the phase transition of the material by replacing some Na-ions with Li-ions. The question remaining is how much Li is required to prevent the phase transition from occurring. The structure of PBAs highly depends on the alkali cation size with structural distortions observed for larger cations. Thus, neutron diffraction on a range of compositions of Li/Na hybrid PBAs is required to determine the structure of Li-based PBAs, the positions of Li/Na within the structure, and confirm the existence of tilt distortions in Li-based PBAs. This will aid the understanding of tilt transitions in PBAs and subsequently how to manipulate these to improve the material performance.