Understanding that I -oxidation in carbon nanopores electrodeposits solid iodine calls for a paradigm shift in two aspects. First, increasing the capacity of such systems relies on strategies to increase the pore filling with solid iodine. Second, avoiding self-discharge means reducing the concentration of mobile polyiodide species generated by comproportionation. Until now, confined immobile polyiodides were thought to be responsible for the excellent self-discharge properties of iodine-based energy storage.