Fig. 2: Schematic of self-depassivation process by iodine species.

a Mechanistic diagram of I₂ in Na-Cl₂ battery. Comparison of the main reversible discharge process of Na-Cl₂ battery with and without I^- mediator. b In the original electrolyte system, a thick and uneven film of NaCl was induced by Cl₂ reduction during discharge. The rGO cathode in this condition is called the original cathode, abbreviated OC. c The high activation voltage and large charge voltage polarization of OC Na-Cl₂ battery after 100 cycles. d When I^- is introduced in the electrolyte as a mediator, it could be strongly coordinated with Na⁺, facilitating its incorporation into the NaCl lattice during discharge. This results in a disarrangement of the NaCl and forms sparse, low-crystallinity small NaCl particles, substantially improving the reactivity of NaCl and enabling a self-passivated cathode. Simultaneously, the generated NaI on the electrode is dissolved in the electrolyte, producing I^- to participate in the next reversible cycle with Na⁺ and Cl₂. The rGO cathode in this condition is called the self-depassivated cathode, abbreviated SDC. e The low activation voltage and steady charge curves of SDC Na-Cl₂ battery after 100 cycles.