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

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)/H₂ O 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 H₂ O-based and TEP-based electrolytes on hydrophobic PP separator surfaces. The BPE interface induces Zn²⁺ solvation structure conversion from [Zn(H₂ O)_x ]²⁺ to [Zn(TEP)_n (H₂ O)_y ]²⁺ , where most solvated H₂ O molecules are removed. In [Zn(TEP)_n (H₂ O)_y ]²⁺ , the residual H₂ O molecules can be further constrained by the formation of H bonds between TEP and H₂ O molecules. Consequently, the ionization of solvated H₂ O 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_x V₂ O₅ batteries are assembled based on the BPE and exhibited enhanced cycling performance.