Charge–discharge characteristics of a solid-state Prussian blue secondary cell

A solid-state secondary cell with Prussian blue, i.e., iron (III) hexacyanoferrate (II), as the active material of both the anode and cathode was constructed. The Prussian blue was mixed with graphite powder, potassium chloride and diluted hydrochloric acid to form a thick paste. A Nafion membrane was used as separator. The charge–discharge performance of the cell was studied in galvanostatic mode. For a stabilized cell, the cell voltage was invariably 1.0 V at half-discharge, whereas it varied from 2.0 to 1.0 V at half-charge depending on the charging rate. Double-step chronopotentiometric experiments were also carried out to understand the charge–discharge behaviour. The practical capacity was estimated to be 20 A h/kg from the maximum deliverable current on discharge. The cell was stable up to 60 cycles of charge–discharge and did not show any significant deterioration.