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/Al_xV₂O₅ batteries are assembled based on the BPE and exhibited enhanced cycling performance.