Enabling stable aqueous Zn metal anodes using scandium acetate electrolyte additives

Abstract

The potential of zinc metal anodes (ZMAs) for use in emerging aqueous electrochemical devices like rechargeable zinc-ion batteries and hybrid capacitors is substantial, owing to their high theoretical capacity, low redox potential, non-toxicity, abundant availability, and cost-effectiveness. However, the practical application of ZMAs faces limitations due to issues such as uncontrolled zinc dendrite growth and side reactions. In this study, we demonstrate that simultaneously incorporating scandium ions (Sc³⁺) and acetate anions (Ac⁻) as electrolyte additives into a 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 be 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 mA h cm⁻². Moreover, the Zn‖Cu cell demonstrates a high average coulombic efficiency of 99.4% after 400 plating/stripping cycles at 1.0 mA cm⁻² and 1.0 mA h cm⁻². Notably, when paired with an activated carbon (AC) cathode, Zn‖AC hybrid capacitors maintain a high-specific capacity of 62 mA h g⁻¹ after 10 000 cycles at 1.0 A g⁻¹. The research outcomes indicate that Sc³⁺ in combination with Ac⁻ are promising electrolyte additives for achieving highly stable aqueous ZMAs.