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Revolutionary 'water battery' has almost double the energy capacity of lithium-ion cells

Aqueous batteries, with their non-flammable water-based electrolytes, offer a safer alternative to lithium-ion batteries
Aqueous batteries, with their non-flammable water-based electrolytes, offer a safer alternative to lithium-ion batteries. (CREDIT: Creative Commons)

Aqueous batteries (also known as water batteries), long recognized for their safety due to water-based electrolytes, have struggled to compete with traditional lithium-ion batteries in terms of energy density.

This new study, published in Nature Energy by a research group led by Prof. LI Xianfeng from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), presents a significant leap forward.


The Challenge: Safety vs. Energy Density

Lithium-ion batteries power our portable electronics and are increasingly being explored for electric vehicles. However, their flammable organic electrolytes pose safety risks.

Aqueous batteries, with their non-flammable water-based electrolytes, offer a safer alternative. But they come with a trade-off: lower energy density, meaning they store less energy per unit volume.


The Innovation: Multi-Electron Transfer Cathode

Prof. LI's team addressed this limitation by developing a novel cathode material that utilizes a mixed-halogen solution (iodide and bromide ions) and undergoes a multi-electron transfer reaction.

During charging, iodide ions (I-) are oxidized to iodate (IO3-) on the positive electrode, while generated hydrogen ions (H+) travel to the negative electrode. Discharging reverses the process, with IO3- being reduced back to I-.


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This multi-electron transfer plays a key role. The researchers achieved a specific capacity exceeding 840 Ah/L for the cathode alone.

When combined with a metallic cadmium anode in a full battery configuration, the energy density reached an impressive 1200 Wh/L based on the newly developed catholyte (electrolyte solution for the cathode).


Bromide's Supporting Role

The presence of bromide ions (Br-) in the electrolyte proved crucial. During charging, Br- interacts with I- to form polar iodine bromide (IBr), which readily reacts with water to generate IO3-.

During discharge, IO3- oxidizes Br- to bromine (Br2), which then participates in the electrochemical reaction, promoting a reversible and rapid discharge process. Essentially, the bromide intermediate acts as a catalyst, optimizing the overall reaction and improving both reaction kinetics and reversibility.


Validation and Future Implications

Prof. FU Qiang's group, collaborators on the project, employed techniques like in-situ optical microscopy and Raman spectroscopy to confirm the multi-electron transfer process.

Prof. LI emphasizes the significance of this research: "This study offers a new direction for designing high-energy-density aqueous batteries, potentially expanding their applications in the realm of power batteries."

This study paves the way for a new generation of aqueous batteries with energy densities approaching those of lithium-ion batteries, while maintaining their inherent safety advantages.


The multi-electron transfer cathode design with mixed-halogen electrolytes presents a promising path forward for aqueous battery technology.

For more science news stories check out our New Innovations section at The Brighter Side of News.


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