An in-depth insight of a highly reversible and dendrite-free Zn metal anode in an hybrid electrolyte

Abstract

Zn metal is considered as one of the most promising anodes for aqueous high-energy batteries owing to its high theoretical capacity, low redox potential, abundant resource, and low toxicity. However, Zn metal anodes (ZMAs) still suffer from a few challenging problems such as low irreversibility and dendrite growth during plating/stripping. In this study, we identify and quantify the composition of inactive Zn responsible for capacity loss, which shows that it contains 57 mol% of unreacted Zn⁰ and 43 mol% Zn-containing byproducts. Based on this quantitative result, we developed an environmentally friendly water/glycerol hybrid electrolyte, which enable the dendrite-free plating/stripping of Zn with a high coulombic efficiency of 97.6% over 500 cycles. A symmetric Zn‖Zn cell can be repeatedly plated/stripped for more than 1500 h at 1 mA cm⁻². Glycerol can suppress the side reactions caused by water in the hybrid electrolyte because of the strong binding interactions between glycerol and the Zn metal. The molecular-scale modeling simulations and electrochemical analysis reveal that the dense and uniform Zn electro-deposition is related to the Zn²⁺-solvation-sheath structure. The fundamental understanding of ZMAs in aqueous and hybrid electrolytes opens a viable route for the highly efficient utilization of Zn with high efficiency and safety.