Activation of Sodium Storage Sites in Prussian Blue Analogues via Surface Etching

Abstract

Sodium-ion battery technologies are known to suffer from kinetic problems associated with the solid-state diffusion of Na⁺ in intercalation electrodes, which results in suppressed specific capacity and degraded rate performance. Here, a controllable selective etching approach is developed for the synthesis of Prussian blue analogue (PBA) with enhanced sodium storage activity. On the basis of time-dependent experiments, a defect-induced morphological evolution mechanism from nanocube to nanoflower structure is proposed. Through in situ X-ray diffraction measurement and computational analysis, this unique structure is revealed to provide higher Na⁺ diffusion dynamics and negligible volume change during the sodiation/desodiation processes. As a sodium ion battery cathode, the PBA exhibits a discharge capacity of 90 mA h g^-1, which is in good agreement with the complete low spin Fe^LS(C) redox reaction. It also demonstrates an outstanding rate capability of 71.0 mA h g^-1 at 44.4 C, as well as an unprecedented cycling reversibility over 5000 times.