Scientists left water inside a battery and nearly doubled its power

Sodium ion batteries could offer a more sustainable way to store large amounts of energy, and new research suggests they may eventually serve another valuable purpose: helping remove salt from seawater.

Scientists at the University of Surrey have found that a sodium-based battery material performs much better when its natural water content is left in place. Battery researchers often remove this water because moisture is commonly viewed as harmful to battery materials. In this case, however, keeping it produced a dramatic improvement.

A More Abundant Alternative to Lithium

Lithium-ion batteries currently power most smartphones, laptops, electric vehicles, and many large energy storage systems. They can store substantial amounts of energy, but lithium and some of the other materials used in these batteries can be expensive to obtain and may carry significant environmental costs.

Sodium is far more common and broadly distributed. It is found in seawater, salt deposits, and many minerals, which makes it an attractive candidate for lower-cost energy storage. Sodium ion batteries operate in a broadly similar way to lithium ion batteries, with charged sodium particles moving between two electrodes as the battery charges and discharges.

The main obstacle has been performance. Many sodium ion battery materials cannot yet match lithium ion technology in how much charge they store, how quickly they charge, or how long they remain useful.

Leaving Water in the Material Boosted Performance

In a study published in the Journal of Materials Chemistry A, the researchers examined sodium vanadium oxide, a sodium-containing material that has been studied for years.

Their focus was a form called nanostructured sodium vanadate hydrate (NVOH). The word hydrate means that water molecules are built into the material's structure. Nanostructured refers to features engineered at an extremely small scale, where changes in shape and arrangement can strongly affect how ions move through a battery.

Instead of heating the material to drive out the water, the team tested what would happen if the water remained.

The result was a major improvement. The hydrated material stored far more charge, charged much faster, and continued to perform reliably for more than 400 charge cycles. A charge cycle represents one complete use of a battery, from charging to discharging and back again.

In laboratory tests, the water-containing version held almost twice as much charge as typical sodium-ion materials. That level of performance placed it among the strongest cathode materials reported for this type of battery.

A cathode is one of a battery's two main electrodes. It plays a central role in storing and releasing charged particles, so improving the cathode can significantly increase the battery's overall capacity and performance.

Dr. Daniel Commandeur, Research Fellow at the University of Surrey School of Chemistry and Chemical Engineering, and lead author of the paper, said:

"Our results were completely unexpected. Sodium vanadium oxide has been around for years, and people usually heat-treat it to remove the water because it's thought to cause problems. We decided to challenge that assumption, and the outcome was far better than we anticipated. The material showed much stronger performance and stability than expected and could even create exciting new possibilities for how these batteries are used in the future."

The Battery Material Also Worked in Salt Water

The researchers then placed the material in salt water, an especially demanding environment for battery components. Salt water can trigger unwanted chemical reactions and interfere with the movement of ions, making it difficult for many materials to function properly.

Despite those conditions, the sodium vanadate hydrate continued to work effectively.

The system also began removing dissolved salt. The sodium-based material pulled sodium from the water, while a graphite electrode removed chloride. Sodium and chloride are the two main charged components of common salt.

This process is known as electrochemical desalination. Instead of using only pressure or heat to separate salt from water, electrochemical desalination uses electrical reactions and specially selected electrodes to draw charged salt particles out of the solution.

Dr. Commandeur added:

"Being able to use sodium vanadate hydrate in salt water is a really exciting discovery, as it shows sodium-ion batteries could do more than just store energy -- they could also help remove salt from water. In the long term, that means we might be able to design systems that use seawater as a completely safe, free and abundant electrolyte, while also producing fresh water as part of the process."

An electrolyte is the substance that allows charged particles to travel between a battery's electrodes. Most commercial batteries use specially formulated liquid or solid electrolytes. If seawater could eventually serve that role safely and effectively, it could reduce material costs while adding a second function to the system.

One Technology Could Store Energy and Produce Fresh Water

The findings raise the possibility of future devices that combine energy storage with water treatment. Such systems could potentially store electricity from solar panels or wind turbines while also removing salt from seawater.

That could be especially useful in coastal regions where access to fresh water is limited but seawater and renewable energy are readily available. However, the research is still at an early stage, and more testing will be needed before the approach can be used in commercial batteries or large desalination systems.

The discovery could also strengthen the case for sodium ion batteries as an alternative to lithium-based technology. Because sodium is abundant and relatively inexpensive, sodium ion systems could become a safer and more sustainable option for storing renewable energy on the electrical grid or powering electric vehicles.

The Surrey team's method may also simplify battery production. Rather than adding another manufacturing step to remove water from the material, manufacturers could potentially leave it in place while gaining better performance.

By challenging a long-standing assumption about moisture, the researchers found a straightforward way to improve an existing battery material. Their results bring high-performance sodium-ion energy storage closer to practical use and hint at a future in which one device could both store clean energy and help turn seawater into fresh water.

Reporting from ScienceDaily contributed to this story.