Iodine-induced self-depassivation strategy to improve reversible kinetics in Na-Cl₂ battery

Rechargeable sodium-chlorine (Na-Cl₂) batteries show high theoretical specific energy density and excellent adaptability for extreme environmental applications. However, the reported cycle life is mostly less than 500 cycles, and the understanding of battery failure mechanisms is quite limited. In this work, we demonstrate that the substantially increased voltage polarization plays a critical role in the battery failure. Typically, the passivation on the porous cathode caused by the deposition of insulated sodium chloride (NaCl) is a crucial factor, significantly influencing the three-phase chlorine (NaCl/Na⁺, Cl^-/Cl₂) conversion kinetics. Here, a self-depassivation strategy enabled by iodine anion (I^-)-tuned NaCl deposition was implemented to enhance the chlorine reversibility. The nucleation and growth of NaCl crystals are well balanced through strong coordination of the NaI deposition-dissolution process, achieving depassivation on the cathode and improving the reoxidation efficiency of solid NaCl. Consequently, the resultant Na-Cl₂ battery delivers a super-long cycle life up to 2000 cycles.