Maintaining the Concentration Equilibrium of Proton and Hydroxide Ions by Construction of Bis(2-Aminoethyl)Amine-Based Inner Helmholtz Plane Toward Long-Life Zinc Metal Anodes

Abstract

Rechargeable aqueous Zn metal batteries have the merits of high safety and low cost. Nevertheless, their development is oppressed by the short cycling life of Zn metal anodes. Because the decomposition of H2O molecules adsorbed in the inner Helmholtz plane (IHP) of Zn metal anodes induces the hydrogen evolution reactions and the formation of irreversible Zn4SO4(OH)6∙nH2O. We herein use bis(2-aminoethyl)amine (B2AA) organic molecules as additives to reconstruct the IHP and maintain the concentration equilibrium of proton and hydroxide ions. Density functional theory calculations and molecule dynamics simulations reveal that B2AA are preferentially adsorbed on the interface of Zn anode owing to the high adsorption energy, forming a water-deficient IHP via repelling ≈19% of H2O molecules. Additionally, the −NH2/−NH− groups of B2AA can reversibly capture H+ derived from the decomposition of H2O and dynamically neutralize OH−, thus suppressing the corrosion reaction. Using an aqueous electrolyte involving B2AA, symmetric Zn//Zn cells exhibit a long cycling life of 2400 h at 10 mA cm−2. Matched with a NH4V4O10 (NVO) cathode, the Zn//NVO full cell delivers a high initial capacity of 147.24 mAh g−1 at 10 A g−1, and maintains a high capacity retention of 66.04% after 3000 cycles.

Keywords: bis(2-aminoethyl)amine-based inner Helmholtz plane, concentration equilibrium of proton and hydroxide ions, trapping protons, neutralizing hydroxide ions, long-life aqueous zinc metal anodes