DOI:
Authors:
Claudia Islas-Vargas, A. Guevara-García, M. Oliver-Tolentino, G. Ramos-Sánchez, I. González, M. Galván
Abstract:
K 2 Zn 3 [Fe(CN) 6 ] 2 was investigated as a cathode for K-ion batteries and compared to its sodium analog. The hexacyanometallate using K + as intercalating ion shows interesting electrochemical properties: i ) The redox processes occur at higher potentials, ii ) From the two redox processes, the one occurring at higher potentials displays most of the specific capacity while the insertion of sodium occurs mostly at lower potentials, iii ) the specific capacity of both materials is similar and iv ) although the hysteresis at higher potentials is higher with K + than with Na + , the occurrence of deintercalation at higher potentials presents undoubtedly more advantages. In the attempt to explain this behavior, electronic structure calculations show that a transition from insulating to conducting behavior occurs as the system changes from discharged to charged states. The electronic density distributions of the hosts are similar independently if K + or Na + ions are intercalated. It is found that the inclusion of dispersion interactions is essential to match the intercalation voltages experimentally observed. Thus, dispersion forces are very important to understand the interactions of the ion with the host and should be considered when designing cathodes for K-ion batteries using hexacyanometallate. Electrochemical experiments.— The electrochemical performance of both, hydrated and anhydrous phases, was evaluated with a battery test cell from E-Cell, which is composed of cathode and metallic-sodium (potassium) anode with a saturated solution of APF 6 (1 L of electrolyte made with 1 mol of AP 6 in 1:1 dimethyl carbonate/ethylene carbonate solvent ratio) and a Whatman glass-fiber separator. The cathodes were prepared by mixing 80%wt of A 2 Zn 3 [Fe(CN) 6 ] 2 with 10%wt amorphous carbon (Timcal SuperP Li) and 10%wt polytetrafluoroethylene as binder in N-methyl-2-pyrrolidone. This mixture is placed on an Al foil and finally dried at 60 ◦ C under vacuum for 24 h, all the reagents were provided by Sigma-Aldrich. The electrochemical data were recorded with a potentiostat − galvanostat VMP3 (from Bio-logic).