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

Despite the merits of high safety and low cost, the development of rechargeable aqueous Zn metal batteries is oppressed by the short cycling life of Zn metal anodes, due to the hydrogen evolution reaction (HER) and the formation of irreversible Zn4SO4(OH)6·nH2O that are caused by the decomposition of H2O molecules adsorbed in the inner Helmholtz plane (IHP) of Zn metal anodes. To solve this issue, we herein use bis(2-aminoethyl)amine (B2AA) organic molecules as additives to suppress Zn corrosion and HER via reconstructing the IHP and maintaining the concentration equilibrium of protons and hydroxide ions, thus achieving long-term and highly reversible Zn metal batteries. 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 at 10 A/g, and maintains a high capacity retention of 66% after 3000 cycles.