Rechargeability of solid-state copper cells utilizing cathodes of Prussian blue and Berlin green

Abstract Discharge and cycling performance of solid-state cells using copper metal, copper ion conductor, and iron hexacyanoferrates, Prussian blue (PB) and Berlin green (BG), was studied. The discharge capacities from start (0.58 V) to 0.4 V of the Cu/PB and Cu/BG cells at 100 μA/cell were 1.35 and 1.98 mAh respectively. At this time, cathode efficiencies were 62% for PB and 79% for BG. The Cu/BG cell showed nearly flat discharge- and charge-end voltage curves over 700 cycles, while the Cu/PB cell displayed the very slowly decreasing curves. The cell performance was discussed on the basis of the crystal structure for ionic diffusion and the hopping mechanism through high- and low-spin iron ions for electronic conduction in the cathode materials.