The Construction of Binary Phase Electrolyte Interface for Highly Stable Zinc Anodes

Abstract

Metal zinc is a promising anode candidate of aqueous zinc-ion batteries due to high theoretical capacity, low cost, and high safety. However, it often suffers from hydrogen evolution reaction (HER), dendrite growth, and formation of by-products. Herein, a triethyl phosphate (TEP)/H2O binary phase electrolyte (BPE) interface is developed by introducing TEP-based electrolyte-wetted hydrophobic polypropylene (PP) separator onto the Zn anode surface. The equilibrium of the BPE interface depends on the comparable surface tensions of H2O-based and TEP-based electrolytes on hydrophobic PP separator surfaces. The BPE interface induces Zn2+ solvation structure conversion from [Zn(H2O)x]2+ to [Zn(TEP)n(H2O)y]2+, where most solvated H2O molecules are removed. In [Zn(TEP)n(H2O)y]2+, the residual H2O molecules can be further constrained by the formation of H bonds between TEP and H2O molecules. Consequently, the ionization of solvated H2O molecules is effectively suppressed, and HER and by-products are effectively restricted on Zn anode surfaces in BPE. As a result, Zn anodes exhibit a high Coulombic efficiency of 99.12% and superior cycling performance of 6000 h, which is much higher than the case in single-phase aqueous electrolytes. To illustrate the feasibility of BPE in full cells, the Zn/AlxV2O5 batteries are assembled based on the BPE and exhibited enhanced cycling performance.