Structural Water Enhanced Intercalation of Magnesium Ions in Copper Hexacyanoferrate Nonaqueous Batteries

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Electrochimica Acta

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In this article we investigate copper hexacyanoferrate (CuHCF) as a nonaqueous magnesium ion battery (MIB) cathode, and the positive influence of structural water on its Mg2+ storage properties. The hydrated and dehydrated forms of CuHCF (H- and D-CuHCF) each displayed excellent rate capabilities and extended lifetimes with zero capacity loss. However, H-CuHCF delivers a specific capacity 25% higher than that of D-CuHCF. Cyclic voltammetry and galvanostatic charge discharge reveal a redox reaction present only in the hydrated CuHCF, which accounts for 25% of its total reversible capacity (63 mAh g−1 at 25 mA g−1). Furthermore, ex-situ FTIR reveals that the structural water of H-CuHCF remains in the lattice during charging/discharging. We propose that water provides partial electrostatic screening between the CuHCF lattice and Mg ions, while allowing an additional redox transition to become thermodynamically accessible.


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