Cation effect on the structure and properties of hexacyanometallates-based nanocomposites: Improving cathode performance in aqueous metal-ions batteries

Abstract Thin films of nanocomposites between carbon nanotubes (CNTs) and three different hexacyanometallates (HCMs) – Prussian blue, ruthenium purple (RP) and cobalt hexacyanoferrate (CoHCFe) - were synthesized with different cations: K + , Na + and Li + . The effect of the cations in both the structure and properties of the HCMs was evaluated by several characterization techniques, showing that the nature of the cation is directly related to the size of the channels in the produced HCM structure, as well as to the defect content, the electrochemical behavior, the electrochemical stability and the strength of the interaction between the HCM and the CNTs. Due to the large hydrated radius, Li + produced the more defective and less stable HCMs, while the HCM synthesized with Na + had large porous and organized structure. All those factors deeply affect the performance of the different films when applied as cathodes for aqueous potassium-, sodium- and lithium-ion secondary battery, which depends on the relationship between the size of hydrated ion and the lattice of the HCM structure. The discharge profile and capacity for RP is reported by the first time. CoHCFe-based composites achieved capacities up to 150 mAh g −1 at 0.67 A g −1 rate, with retention of 90% after 2000 cycles.