Trace Sc3+-electrolyte additive enabling stable Zn metal anodes for aqueous zinc-ion batteries

A self-regulated interface enabled by trivalent gadolinium ions toward highly reversible zinc metal anodes

Aqueous zinc-ion batteries (AZIBs) have become an ideal candidate for large-scale energy storage systems owing to their inherent safety and highly competitive capacity. However, severe dendrite growth and side reactions on the surface of zinc metal anodes lead to quick performance deterioration, seriously impeding the commercialization of AZIBs. In this work, a self-regulated zinc metal/electrolyte interface is constructed to solve these problems by incorporating the trivalent Gd3+ additive with a lower effective reduction potential into the aqueous ZnSO4 electrolyte. It is revealed that the inert Gd3+ ions preferentially adsorb on the active sites of the zinc anode, and the induced electrostatic shielding layer is beneficial to uniform Zn deposition. Meanwhile, the adsorbed Gd3+ ions act as a buffer interface to lower the direct contact of the zinc anode with water molecules, thereby suppressing the interfacial parasitic reaction. These features endow the Zn//Zn battery using 0.2 M Gd3+ ions with 2940 h of cycling life at 5 mA cm-2 and a cumulative plating capacity (CPC) of 6.2 Ah cm-2 at 40 mA cm-2. When assembling with a MnO2 cathode, the full cell using the modified electrolyte exhibits a high capacity of 268.9 mAh/g at 0.2 A/g, as well as improved rate capability and cycle stability. The results suggest the great potential of a rare earth ion additive in reinforcing Zn metal anodes for developing practical AZIBs.

A low concentration electrolyte additive for constructing solid-electrolyte interphase on a Zn metal anode for aqueous batteries

Zn metal anodes in aqueous batteries experience inhomogeneous deposition and corrosion issues. Herein, we introduced, at a low concentration, dioxane (DX) as an electrolyte additive to stabilize a Zn anode. The oxygen sites of DX endowed it with a strong affinity for Zn and Zn2+, resulting in its adsorption onto the Zn electrode surface and its coordination with Zn2+ locally. The Zn2+-DX species exhibited a decreased lowest unoccupied molecular orbital energy level relative to those of water-involved components. The DX additive not only inhibited side reactions but also generated a stable solid-electrolyte interphase on the Zn electrode, ensuring a uniform Zn deposition. As a result of including the additive, the cycle life of the Zn symmetric cell was extended from 99 h to 2100 h, and the coulombic efficiency in Zn//Cu cell reached 99.5%.