Unveil the role of structural vacancy in Mn-based Prussian blue for energy storage application

Abstract

Prussian blue analogues (PBAs) are promising cathode materials for monovalent- and multivalent-ion batteries due to the large frame structure. However, the effect of vacancy in lattice on the electrochemical performance has not been clearly elucidated, hindering the further development of PBAs. Here we identify two types of different functional vacancies (defined as structural vacancy and defective vacancy) in Mn-based PBAs (MnHCF) through Synchrotron-based X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculation. In-situ X-ray diffraction (XRD) shows that MnHCF with structural vacancy has a slighter structural evolution than MnHCF with defective vacancy during cycles. The electrochemical results indicate that the defective vacancy in MnHCF deteriorates the cyclic performance, whereas the structural vacancy favors ion diffusion and helps to stabilize the structure. Moreover, the structure with gradient structural vacancy was successfully introduced to K-rich MnHCF, realizing a high capacity and a remarkable improvement in long-term cyclic stability for alkali metal-ion (Li+/Na+/K+) batteries.