How controlling water behavior in deep eutectic solvents solves zinc-ion battery challenges for sustainable energy storage
Imagine a world where renewable energy powers everything—but only when the sun shines or the wind blows. This intermittent nature of clean energy sources represents one of our greatest technological challenges, making advanced energy storage systems crucial for our sustainable future.
Zinc-ion batteries typically use water-based electrolytes, capitalizing on water's safety and excellent ability to conduct ions. So what goes wrong? The answer lies in zinc's relationship with water molecules at the most fundamental level.
"The free water easily reacts with metallic Zn at the electrode/electrolyte interface, leading to a range of parasitic processes that critically impact durability" 3 .
| Problem | Cause | Consequence |
|---|---|---|
| Hydrogen Evolution | Free water molecules reacting with zinc | Gas buildup, pressure increase, potential leakage 3 |
| Passivation | Reaction products forming insoluble layers | Reduced conductivity, increased resistance 3 |
| Shape Changes | Uncontrolled zinc deposition during charging | Dendrite formation, short circuits, reduced cycle life 3 |
Unbound water molecules gather at electrode interface
Water molecules break down, releasing hydrogen gas 3
Insulating films develop on zinc electrode 3
Irregular zinc deposition creates short-circuit risks 3
Deep eutectic solvents represent a fascinating class of materials that offer a potential way out of this dilemma. DES are mixtures of two or more components—typically a hydrogen bond acceptor (such as choline chloride) and a hydrogen bond donor (such as ethylene glycol or urea)—that combine to form a eutectic mixture with a melting point lower than either component alone 3 .
Low toxicity, biodegradability, renewable resources 3
Simple preparation from inexpensive components 3
Enhanced safety with low vapor pressure 3
Tunable properties through component variations
"Alternative electrolytes such as Deep Eutectic Solvents can be used to modulate the Zn solvation shell and limit free water molecules, while still preserving the green and safe characteristics of aqueous-based ones" 3 .
A groundbreaking study published in 2025 systematically investigated how precisely controlling water content in DES electrolytes could transform zinc battery performance 1 3 . The research team designed an elegant experiment to unravel the complex relationship between water, zinc ions, and the electrode interface.
The researchers focused on ethaline—a common DES composed of choline chloride and ethylene glycol in a 1:2 molar ratio—and methodically prepared samples with varying water contents (0 wt%, 1 wt%, 3 wt%, 10 wt%, 20 wt%, and 50 wt%) 3 .
Small water amounts decrease viscosity and increase ion mobility 3
Water incorporates into zinc solvation shell, changing deposition 3
Hydrated DES forms stable electrode-electrolyte interface 3
The Grotthuss mechanism, named after its 1805 discoverer Theodor Grotthuss, allows protons to hop along water molecule networks through hydrogen bond formation and rearrangement, enabling much more efficient charge transport than simple ion diffusion 8 .
| Electrolyte Type | Key Advantages | Limitations | Typical Cycle Life |
|---|---|---|---|
| Conventional Aqueous | High conductivity, safe, low cost | Severe side reactions, dendrite formation | Limited (hundreds of cycles) |
| Pure DES | Minimal side reactions, wide stability window | High viscosity, low conductivity | Moderate but limited kinetics |
| Optimally Hydrated DES | Balanced conductivity & stability, suppressed side reactions | Requires precise water control | Extended (thousands of cycles) 3 |
The implications of this research extend far beyond zinc-ion batteries themselves. Mastering the role of water in DES electrolytes represents a significant step toward sustainable, safe, and cost-effective energy storage solutions that could accelerate our transition to renewable energy.
The dynamic role of water in deep eutectic solvents exemplifies the sophisticated engineering challenges involved in creating the energy storage systems of tomorrow. Water, once considered merely a problem for zinc batteries, now emerges as a potential solution—when properly controlled and precisely balanced within advanced solvent systems.
Precise water control enables optimal performance
Green DES components support eco-friendly solutions
Extended cycle life enables practical applications 3
This research illuminates a path forward where the inherent safety and sustainability of aqueous-based batteries can be preserved while overcoming the limitations that have historically restricted their lifespan. By learning to manipulate materials at the molecular level, we move closer to realizing the full potential of zinc and other abundant metals for our energy storage needs.