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

Prussian blue analogues (PBAs) are promising cathode materials for monovalent- and multivalent-ion batteries due to their large framework structures. Nevertheless, the influence of lattice vacancies on electrochemical performance has not been thoroughly clarified, hindering the further development of PBAs. Here we identify two types of functional vacancies, namely structural vacancy (SV) and incidental vacancy (IV) in manganese hexacyanoferrate (MnHCF) through Synchrotron-based X-ray absorption spectroscopy and density functional theory calculations. Unlike structurally disordered IV, the introduction of structurally ordered SV promotes ion transport and reduces the interaction between host ions and the framework, enabling improved cyclic and rate performance. The controllable adjustment of SV in K-rich MnHCF is achieved through a co-reactant method. Furthermore, the partial introduction of SV in K-rich MnHCF is demonstrated to favor both a milder structural evolution by alleviating the Jahn-teller distortion of Mn³⁺ and a stable dynamic process of interface reaction. This study unveils the potential importance of incorporating structural vacancy into MnHCF for advanced energy storage applications.