Fig. 4: Low self-discharge, high capacity density iodine energy storage.

a Specific capacity versus specific current for galvanostatic charge/discharge with capacity limitation of 160 mAh g_C⁻¹. b WE potential as a function of capacity for the four highest currents with 24.3 A g_C⁻¹ (red), 8.1 A g_C⁻¹ (blue), 2.7 A g_C⁻¹ (gray), 0.9 A g_C⁻¹ (black) of the same galvanostatic charge/discharge measurements. c Charge/discharge capacity and coulombic efficiency versus number of cycles at a rate of 0.3 A g_C⁻¹. The inset shows the WE potential as a function time for 2 cycles. d Potentiostatic charge / discharge (+0.6/0 V vs. Ag/AgCl) measurements with increasing resting times at open-circuit voltage (OCV) between the charging and discharging steps. Potentiostatic charge was limited to 330 mAh g_C⁻¹, potentiostatic discharge to 4 h within which the current always dropped to negligible values. The protocol is exemplified for the 1 M NaI electrolyte and a charging capacity of 330 mAh g_C⁻¹. e Discharge capacities vs. resting times for the protocol shown in a using the 1 M NaI electrolyte and two different charging capacities (219 mAh g_C⁻¹ and 330  mAh g_C⁻¹) and the 0.5 M NaI + 0.5 M NaNO₃ electrolyte with a charging capacity of 330 mAh g_C⁻¹. The right axis shows the iodine pore occupancy, estimated from the discharge capacities and the known electrode porosity values.