Ultrathin formvar film protective layer via simple dipping strategy for ultra-stable zinc-metal anodes

Aqueous Zn ion batteries (ZIBs) have become a strong competitor in the field of large-scale energy storage. However, surface side reactions, such as Zn corrosion, hydrogen evolution reaction, and dendrite growth, lead to low reversibility of Zn anode. This study introduces a time-saving and simple solution-dipping method to address above issues by spreading ultrathin Poly (vinyl formal) (PVF) protective layer on the surface of Zn anode (denoted as PVF@Zn). Owing to its abundant oxygen-containing functional groups, PVF molecule exhibits not only highly adhesive force with Zn metal surface but also higher zincophilicity with Zn²⁺ ions. The former effectively prevents direct contact between electrolyte and Zn anode as well as guides a three-dimensional (3D) diffusion mode of Zn²⁺ plating, the latter reduces the Zn nucleation energy barrier as well as enhances the uniformity of Zn deposition. Meanwhile, the hydrophilic and ion conductivity characters endow the PVF film with abundant nucleation sites and homogenous electric field distribution, further guaranteeing an even Zn deposition. Moreover, the outstanding mechanical strength and elasticity of the PVF film can withstand the volume variation during Zn plating/stripping, which is conducive to inhibit the growth of dendrites. Consequently, symmetrical cells assembled by the PVF@Zn electrodes deliver dendrite-free plating/stripping and an ultra-long stable cycle of 4900 h at 0.5 mA cm^-2, 1.0 mAh cm^-2. Even though the current density is as high as 10 mA cm^-2, the PVF@Zn electrode still possesses a cycling life of 4000 h and the corresponding cumulative plating capacity is up to 20,000 mAh cm^-2. When paired with a MnO₂ cathode, the PVF@Zn anode retains 72.5 % capacity over 1000 cycles at 1 A g^-1, which is much better than that of bare Zn (18.4 %). This work provides a promising method for rapidly fabricating ultrathin Zn anode protective layer to inhibit dendrites and side reactions in aqueous Zn ion battery.