An immiscible phase-separation electrolyte and interface ion transfer electrochemistry enable zinc/lithium hybrid batteries with a 3.5 V-class operating voltage

The low-cost and high safety of zinc batteries have attracted tremendous attention in recent years. However, with conventional electrolytes, the operating voltages of zinc batteries are normally below 2 V. Hybrid batteries represented by commercial zinc-nickel batteries (zinc-proton hybrid batteries) employ H⁺ as the charge carrier to obtain a high operating voltage and electrochemical performance. Nevertheless, the preparation of other alkaline zinc-based hybrid batteries with high electrochemical performance is difficult to achieve due to the narrow cathodic window and incompatibility of cathode materials with the alkaline electrolyte. Herein, we develop a unique phase-separation electrolyte (PSE) consisting of a completely immiscible aqueous phase and an oil phase. The alkaline aqueous electrolyte can take advantage of the low electrode potential of the zinc anode. The interface ion transfer electrochemistry in the PSE can further boost the operating voltage by & SIM;0.35 V. Accordingly, our developed zinc/lithium hybrid batteries deliver an unprecedented average operating voltage of 3.41 V and a high energy density of 362.4 W h kg_{anode+cathode}^-1 (N/P is assumed to be 1), approaching the voltage of lithium-ion batteries. More interestingly, the liquid-liquid interface in the PSE can entirely intercept the propagation of zinc dendrites, benefiting from the completely blocked diffusion of Zn²⁺ into the oil phase. Zinc/lithium hybrid batteries with LiMn₂O₄ cathodes deliver an excellent cycle performance over 600 cycles with a 99.6% coulombic efficiency. To further demonstrate practicality, we fabricated a full cell with a commercial-level cathode mass loading of 18.3 mg cm^-2, achieving a zinc-based battery with a high voltage of 2.56 V and a high areal capacity of 2.14 mA h cm^-2. © The Royal Society of Chemistry 2023