Enabling Stable Aqueous Zn Metal Anodes by Scandium Acetate Electrolyte Additives

Abstract

The potential of zinc metal anode (ZMA) in emerging aqueous electrochemical devices like rechargeable zinc-ion batteries and hybrid capacitors is substantial, owing to its high theoretical capacity, low redox potential, non-toxicity, abundant availability, and cost-effectiveness. However, the practical application of ZMA faces limitations due to issues such as uncontrolled zinc dendrites growth and side reactions. In this study, we demonstrate that simultaneously incorporating scandium ion (Sc3+) and acetate anion (Ac‒) as electrolyte additives in the common ZnSO4 solution significantly enhances the cycling stability and reversibility of ZMAs. Our findings reveal that the Ac‒ acts as a pH regulator, dynamically buffering the electrolyte pH to around 4.3, effectively suppressing water-induced side reactions. Additionally, the synergistic effect of Sc3+ and Ac‒ (Sc3+/Ac‒) facilitates the desolation process of Zn2+ and lowers the energy barrier for electrochemical Zn plating, resulting in uniform Zn plating without noticeable zinc dendrite growth. Consequently, Zn‖Zn symmetric cells utilizing the Sc3+/Ac‒ electrolyte additive exhibit an ultra-long lifespan exceeding 1000 hours at 2.0 mA cm‒2 and 1.0 mAh cm‒2. Moreover, the Zn‖Cu cell demonstrates a high average Coulombic efficiency of 98.45% after 400 plating/stripping cycles at 1.0 mA cm‒2 and 1.0 mAh cm‒2. Notably, when paired with an activated carbon (AC) cathode, Zn‖AC hybrid capacitors maintain a high-specific capacity of 62 mAh g‒1 after 10,000 cycles at 1.0 A g‒1. The research outcomes indicate that Sc3+ cooperated with Ac‒ are the promising electrolyte additive for achieving highly stable aqueous ZMAs.