How Prussian Blue Analogues Can Be Stable in Concentrated Aqueous Electrolytes

Prussian blue analogues (PBAs) are promising candidates for storing various ions in aqueous electrolytes. But they often suffer from metal-ion dissolution induced structural degradation, resulting in fast capacity fade and short cycle life. Long-term cycling of PBAs has recently been successfully demonstrated by using highly concentrated aqueous electrolytes, while the stabilization mechanism of PBAs in the electrolytes has remained unclear. In this work, the experimental and molecular modeling evidence indicates that the hydrophobic layer on the PBA/electrolyte interface and the highly restricted network in the concentrated aqueous electrolyte both play critical roles in suppressing metal-ion dissolution of PBAs. That explains why the NH4+ full battery consisting of a PBA cathode can be stably cycled over 4000 cycles with 72.3% capacity retention (8C). The molecular-level understanding of the stabilization mechanism establishes a guiding principle for the stable storage of diverse ions in PBAs, including but not limited to NH4+, Li+, Na+, Mg2+, etc.