Biphasic Electrolyte Engineering Enabling Reversible Zn Metal Batteries

Aqueous Zn metal batteries are promising for large-scale energy storage. However, their implementation is limited by the irreversible Zn anodes. Herein, the biphasic electrolyte based on the "salting out" effect is proposed to comprehensively enhance the electrochemical performance. The organic-rich phase electrolyte on the Zn anode side not only decreases the water content but also manipulates the Zn2+ solvation structure. Additionally, a uniform ZnOHF solid-electrolyte interphase (SEI) is formed in situ. This synergy contributes to suppressing water-triggered parasitic reactions and dendrite growth, resulting in a high average Coulombic efficiency (99.68% over 400 cycles) and prolonged cycling lifespans. On the cathode side, the aqueous phase electrolyte maintains fast ionic conductivity and modifies the electrode/electrolyte interface property because of residual organic molecules, which accelerates the redox kinetics. The Zn//PANI full cell with biphasic electrolyte performs much better with regard to rate, cycling, and storage performance than a cell with a conventional aqueous ZnSO4 electrolyte.