A Novel Strategy to Improve the Electrochemical Performance of a Prussian Blue Analogue Electrode for Calcium-Ion Batteries

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Herein, mixtures of water and propylene carbonate (PC) containing Ca(CF₃SO₃)₂ were used as electrolytes to improve the electrochemical performance parameters of a Prussian blue analogue electrode, copper hexacyanoferrate, for use in calcium-ion batteries. The performance of the electrode was greatly influenced by the molar ratio of the two solvents (water and PC) in the electrolyte. The electrode exhibited a relatively high capacity when the molar ratio of calcium cations to water in the electrolyte was 1:6. In addition, the electrode exhibited a coulombic efficiency of ∼100% over 800 cycles, with ∼94% retention of the maximum capacity after 800 cycles in this electrolyte solution. Raman spectroscopy revealed that calcium cations were preferentially solvated by water molecules in the electrolyte, which is believed to be related to the improvement in electrode performance.