Compensating effect of self-assembled capsule towards enhanced structural stability of prussian blue cathodes for sodium-ion batteries

The Prussian Blue analog (PBA) is a promising sodium-ion cathode material with high theoretical capacity and relatively easy to synthesize. One of the Prussian Blue analogs, sodium manganese hexacyanoferrate (NaxMn[Fe(CN)(6)], MnHCF), experiences significant initial capacity decrease due to Jahn-Teller distortion depending on the sodium content. In contrast, Sodium copper hexacyanoferrate (NaxCu[Fe(CN)(6)], CuHCF) exhibits lower reversible sodium-ion content compared to MnHCF and exhibits excellent cycling stability. We designed direct-strike coprecipitation process to synthesize nanocomposite of PBAs. The proposed encapsulated composite has been successfully synthesized by encapsulating MnHCF with self-assembled CuHCF, leading to substantial improvement in the cycling performance of MnHCF. The encapsulated composite demonstrated a capacity of 106.2 mAh g(-1) even at high current rate. Regarding cycle stability, it retained over 68 % of its initial capacity even after 500 cycles. The ion conductivity was calculated through the Galvanostatic intermittent titration test (GITT), and the encapsulated composite exhibited higher ion conductivity than pristine MnHCF. Ex-situ post-analysis was conducted to confirm structural evolution of samples. The severe structural collapse of MnHCF led to electrode damage, whereas the encapsulated composite demonstrated excellent electrode condition. The encapsulated composite exhibited superior performance in full-cell tests as well.