Researchers in China report a universal strategy to expand the design space of aqueous electrolytes for zinc batteries, achieving a 3.8-volt stability window and ultra-long cycling life of over 10,000 cycles.
Aqueous batteries are widely regarded as a promising solution for safe and affordable energy storage. Yet their development has long been constrained by a fundamental limitation: the narrow electrochemical stability window of water-based electrolytes, which restricts battery voltage and energy density. The “water-in-salt” (WiS) strategy—using ultrahigh salt concentrations to suppress water activity—has been a major breakthrough. However, its application has been largely limited to a handful of salts with exceptionally high solubility, making the approach less generalizable. Now, a team led by Professor Chaoji Chen and Associate Researcher Le Yu at Wuhan University’s School of Resource and Environmental Sciences has introduced a new class of electrolytes that overcomes this bottleneck. By incorporating ionic liquids—salts that are liquid at room temperature—the researchers formulated a series of “water-in-salt/ionic liquid” (Wi(S/IL)) electrolytes that work with commonly used zinc salts, greatly expanding the material options for high-performance aqueous batteries.“Ionic liquids are unique because they can function both as a salt and as a solvent,” said Yu, the paper’s co-first author and corresponding author. “This dual role allows us to create stable, homogeneous electrolytes even with zinc salts that are normally poorly soluble in water.”The team systematically screened 25 combinations of five common zinc salts and five ionic liquids, and found that 16 of them could form stable Wi(S/IL) electrolytes that meet the low water-to-salt ratio required for the WiS regime.
A closer look at liquid structure
To understand why these new electrolytes perform so well, the researchers developed a comprehensive analytical approach combining infrared spectroscopy, nuclear magnetic resonance, Raman spectroscopy, electrospray ionization mass spectrometry, and synchrotron small-angle X-ray scattering. This multi-technique strategy allowed them to map, with unprecedented detail, how water molecules and zinc ions are organized in the electrolyte—from the immediate solvation shells around the ions to long-range molecular arrangements.“We were able to trace exactly where water molecules go as we reduce the water content,” explained Sijun Wang, a doctoral student and co-first author of the study. “In our Wi(S/IL) system, water molecules are progressively displaced from the zinc ion’s primary solvation sheath by the ionic liquid’s anions, creating a unique anion-dominated environment.”This anionic solvation structure is fundamentally different from conventional WiS electrolytes, where water typically remains in direct contact with the metal ions. The difference is attributed to the strong electrostatic interactions between zinc ions and the bulky, charge-delocalized anions of the ionic liquid.
Exceptional performance
The structural insights translated directly into outstanding electrochemical performance. The Wi(S/IL) electrolyte demonstrated an exceptionally wide electrochemical stability window of 3.8 volts, one of the highest reported for aqueous zinc systems. In zinc-copper cells, it achieved an average Coulombic efficiency of 99.7% for zinc plating and stripping over 680 cycles. In full zinc-vanadium oxide batteries, the system maintained stable operation for more than 10,000 cycles, corresponding to a lifespan of over one year. The team also identified the chemical origin of this stability. During cycling, the ionic liquid’s cations and anions decompose at the zinc surface to form a robust, organic-inorganic hybrid layer—a solid-electrolyte interphase that physically blocks water molecules while allowing zinc ions to pass through efficiently.
A new paradigm for electrolyte design
Beyond the high-performance electrolyte itself, the study offers a broader methodological advance. The analytical workflow developed by the researchers provides a systematic way to decode the often-complex liquid structures of concentrated electrolytes, enabling more predictable design of electrolyte formulations.“Our approach moves electrolyte research from a trial-and-error process toward rational design,” said Chen, the corresponding author. “By understanding exactly how molecules arrange themselves at different scales, we can more reliably achieve desired electrochemical properties.”
The work is published in the journal National Science Review .
National Science Review
Experimental study