A Self-Phase Separated Electrolyte toward Durable and Rollover-Stable Zinc Metal Batteries.

Aqueous zinc (Zn) metal batteries (ZMBs) have received great attention due to their safety and environmental friendliness. Although aqueous electrolytes facilitate fast kinetics in metal oxide cathodes, their incompatibility with the Zn metal anodes triggers severe hydrogen evolution reaction (HER) and dendrite growth. Herein, a self-phase separated electrolyte (SPSE) is proposed to fulfill the contradictory requirements of the anode and cathode in ZMBs. Molecular modeling and experimental investigations verify that the hydrophobic fluorinated solvent with moderate dielectric constant and large Hildebrand parameter disparity relative to water contributes to a spontaneous aqueous-nonaqueous phase separation within the SPSE against stirring and aging. In the as-developed SPSE, the anode nonaqueous phase effectively inhibits the HER and dendrite formation by a synergistic effect of regulated Zn deposition and protective solid electrolyte interphase (SEI). Meanwhile, the aqueous phase in the cathode ensures fast ion insertion/extraction dynamics. Consequently, the SPSE allows for Zn||Zn symmetrical cells with 2500 h cycle life and ultralow corrosion current (0.08 mA cm). Notably, the Zn|SPSE|VO full cell sustains over 3000 cycles with negligible HER and corrosion, and the pouch cell demonstrates remarkable operation stability against repeated rollover. Our electrolyte design concept paves a promising path for practical ZMBs that combine long-term cyclability, enhanced safety, and durability.