Tunable Zn de-solvation behavior in MnO cathodes self-assembled phytic acid monolayers for stable aqueous Zn-ion batteries.

Sluggish ion diffusion kinetics at the electrode/electrolyte interface leads to insufficient rate capability and poor structural reversibility, which are mainly attributed to the hydrated Zn migration process being inhibited due to its huge de-solvation energy barriers. Herein, a self-assembly method is proposed in which a multifunctional monolayer with phytic acid (PA) is coated on the surface of MnO strongly attaching to the substrate with the formation of chemical bonding to effectively prevent the dissolution of PA in the electrolyte. Due to the negative charge and inherent ultra-hydrophilicity of PA, modified MnO demonstrates stronger adsorption of positive ions and captures reactive water molecules, easily accelerating the de-solvation process of interfacial hydrated Zn, efficiently achieving reversible Zn insertion/extraction. Meanwhile, the coating layers can protect the substrate from attack by active water molecules, thus inhibiting cathode dissolution during battery cycling. Experimental characterization studies reveal that the protected MnO cathode exhibits a remarkable specific capacity of 273 mA h g with a zinc intercalation capacity contribution of more than 60% at a current density of 0.1 A g. Additionally, even at a high current density of 1 A g, it maintains a capacity of 197 mA h g, far exceeding that of pure MnO. Furthermore, the Zn-ion pouch cell, serving as a proof of concept, achieves an impressive energy density of 300 W h kg and exhibits remarkable capacity retention of 77% even after 100 cycles. This work offers a universal strategy for expediting the de-solvation process of hydrated Zn on the surface of manganese-based cathodes in aqueous zinc-ion batteries.