Revitalizing Dead Zinc with Ferrocene/Ferrocenium Redox Chemistry for Deep-Cycle Zinc Metal Batteries

Aqueous zinc (Zn) batteries are highly desirable for sustainable and large-scale electrochemical energy storage technologies. However, the ceaseless dendrite growth and the derived dead Zn are principally responsible for the capacity decay and insufficient lifespan. Here, we propose a dissolved oxygen-initiated revitalization strategy to reactivate dead Zn via ferrocene redox chemistry, which can be realized by incorporating a trace amount of poly(ethylene glycol) as a solubilizer to improve the solubility of water-insoluble ferrocene derivatives. Ferrocene scaffold can be spontaneously oxidized to ferricenium cations by dissolved oxygen, which eradicates the dissolved oxygen-involved Zn corrosion and insulating by-product generation. Subsequently, the generated ferricenium cations as the scavenger can rejuvenate electrically isolated dead Zn into electroactive Zn²⁺ ions to compensate the zinc loss. Through this design, the symmetric cell exhibited improved cycle life of 3700 h at 10 mA cm^-2, and 220 h under a high depth of discharge of 80 %. Importantly, the Zn||NaV₃O₈ ⋅ 1.5H₂O full cells demonstrated the impressive cycling stability over 1500 cycles at a low N/P ratio of 3.0. This work presents an innovative solution for the revitalization of dead Zn to extend the lifespan of deep-cycling metal batteries.