Phase transformation of copper hexacyanoferrate (KCuFe(CN)6) during zinc insertion: Effect of co-ion intercalation

Aquoeus zinc-ion batteries have become an interesting alternative to the traditional technologies used for energy storage from renewable energy sources. Among them, systems based on Prussian Blue derivates have attracted great attention due to their high discharge potential, good cyclability and rate capability. In this work we have observed that both anion and co-cations are playing a critical role in the cycle stability of copper hexacynoferrate. By using post-mortem X-ray diffraction, it is observed that a partial transformation of copper hexacyanoferrate structure occurs via substitution of the transition metals in the lattice. The phase transformation mitigate the energy losses, and in certain conditions allows retaining up to 82% of the initial energy provided after 500 cycles.