A stable fluoride-based interphase for a long cycle Zn metal anode in an aqueous zinc ion battery

Abstract

Currently, rechargeable aqueous zinc ion batteries (AZIBs) have attracted extensive attention as a promising energy storage system to replace the traditional lithium-ion batteries because of their high energy density, low cost, high safety, and convenient assembly. However, zinc dendritic growth and side reactions on the Zn metal surface limit their practical applications. Herein, we firstly developed stable fluoride-based interphase to address these issues by coating a dense CaF₂ layer on the Zn surface as a protective layer. The CaF₂ layer is an insulator whose corrosion resistance and low polarization facilitate the diffusion of Zn ions and the suppression of hydrogen evolution, resulting in low interfacial impedance of electrodes. The lower binding energy of the interface calculated using density functional theory (DFT) was beneficial for adsorbing Zn²⁺ due to the electronegative F atoms, forming strong interactions with the Zn atoms. Moreover, the protection layer vastly reduces the nucleation energy barrier and the nucleation overpotential of Zn²⁺ ions. Encouragingly, the Zn anode with a CaF₂ layer exhibits an ultra-long cycle life (more than 4000 h) in a Zn//Zn symmetrical cell, which is far superior to other interphase modification strategies with inorganic compounds. The Zn@CaF₂//V₁₀O₂₄ full battery maintains a capacity of 70% (133 mA h g⁻¹) after 1000 cycles even at a large current density of 2 A g⁻¹, which is much higher than that of the Zn//V₁₀O₂₄ full battery (33 mA h g⁻¹). CaF₂ as a durable protective layer on the Zn anode surface provides a practical approach for dendrite-free Zn anodes and high-performance AZIBs.