Bicontinuous-phase electrolyte for a highly reversible Zn metal anode working at ultralow temperature†

Abstract

Hybrid electrolytes utilizing organic solvents as cosolvents or additives present tremendous promise for low-temperature aqueous zinc ion batteries (ZIBs). However, the nanostructure of hybrid electrolytes has been rarely investigated, leaving a knowledge gap between the atomistic solvation structure and macroscopic battery performance. Herein, the nanostructure of hybrid electrolytes was systematically studied, and a new concept of bicontinuous-phase electrolyte (BPE) is proposed. By carefully adjusting the volume ratio of H₂O and organic solvent, a BPE with a three-dimensional interpenetrating aqueous phase and organic phase is obtained, which delivers an optimal Zn²⁺ transfer number of 0.68 and fast desolvation kinetics. More importantly, the BPE possesses a well-balanced organic solvent-rich solvation sheath and anion-involved solvation sheath and generates a uniform in situ solid electrolyte interface with an organic-rich outer layer and inorganic-rich inner layer. The BPE affords ultralong cycling stability for about 4700 hours at −20 °C and boosts stability at an ultralow temperature of −60 °C, outperforming most low-temperature ZIBs. Equally intriguingly, the Zn anode exhibits record-breaking reversibility over 13 000 hours at room temperature. Impressively, Zn‖V₂O₅ batteries show an excellent capacity retention of 100% for over 1100 cycles at −60 °C and over 2000 cycles under high mass loading (14 mg cm⁻²), lean electrolyte conditions (E/C ratio = 8.7 μL mA⁻¹ h⁻¹), and limited Zn supply (N/P ratio = 2.55). This study provides an in-depth understanding of the nanostructures of hybrid electrolytes, which opens a universal avenue toward high-performance low-temperature batteries.