A Fluorine-Free Electrolyte with Copper Ion-Guided Interfacial Regulation Enables Ultra-Stable Zinc Metal Batteries

Non-aqueous zinc metal batteries offer a promising pathway toward high energy density and long-lasting energy storage systems, yet their practical implementation is hindered by dendritic growth and unstable electrode-electrolyte interfaces. Herein, we report a fluorine-free organic electrolyte based on zinc methanesulfonate (ZMS), (Zn(MeSO3)2, in N,N-dimethylformamide (DMF), coupled with a copper ion (Cu2+) additive to regulate the zinc (Zn) deposition via interfacial engineering. The ZMS salt provides a tunable electrolyte environment, while the Cu2+ additive undergoes a spontaneous galvanic replacement reaction with Zn, forming a Cu-based interfacial layer. This interfacial modification promotes uniform Zn nucleation and suppresses dendritic growth. The optimized 5 mM CuSO4 electrolyte delivers 99.88% CE and enables ultra-stable Zn||Zn cycling (>2000 h), while sustaining operation up to 20 mA cm-2. The complementary spectroscopic and electrochemical analyses support the formation of a Cu-based interfacial layer and reveal modified methanesulfonate transport in the Cu2+-containing electrolyte. The full cells with both NaV3O8 and PANI cathodes achieve 74.2% capacity retention (relative to first-cycle capacity) over 300 cycles and 92.6% retention over 800 cycles, respectively, demonstrating proof-of-concept full-cell compatibility of this fluorine-free electrolyte formulation with different cathode chemistries.