Why Structural Water Matters
Sodium’s Growing Appeal as a Lithium Alternative
A Balance Between Capacity and Stability
Beyond Batteries: A Role in Water Desalination
Redefining Materials Design
References and Further Reading
In battery research, water is regarded as a destructive element. Moisture can accelerate degradation, promote unwanted side reactions, and reduce long-term device stability. This is why manufacturers remove water during electrode production. However, new research from the University of Surrey challenges this. The team deliberately retained crystalline water and found that it improved electrochemical performance, opening new possibilities for sodium-ion batteries and electrochemical desalination technologies.1
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The University of Surrey team focused on nanostructured sodium vanadate hydrate (NaV3O8.xH2O or NVOH), a layered material capable of storing sodium ions. Structural water sits in the lattice and widens vanadium-oxide layers, creating larger channels that allow sodium ions to move during charge–discharge cycles. This improves sodium-ion transport and storage compared with dried materials.
Why Structural Water Matters
The key discovery centers on the distinction between free water and structural water. Structural water is not simply trapped moisture; it resides within the crystal lattice and helps define the material's geometry.
In NVOH, water molecules increase the spacing between the vanadium oxide layers, creating wider channels through which sodium ions can move and intercalate during charge-discharge cycles.1
This expanded interlayer structure proved highly beneficial. Samples that kept their crystalline water achieved a specific capacity of 280 mAh per gram at a low current density of 10 mA per gram, considerably higher than many previously reported sodium vanadate materials that underwent thermal drying treatments.1 The wider spacing effectively creates additional room for sodium ions, improving storage capacity while maintaining favorable ion transport characteristics.
The findings align with a growing body of research showing that interlayer engineering can dramatically influence battery performance. Previous studies have demonstrated that controlling crystal structure and intercalation pathways is often as important as the chemical composition of the electrode material itself.2,3 The Surrey work extends this concept by illustrating how water molecules can serve as structural components that enhance electrochemical functionality rather than diminish it.1
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Sodium’s Growing Appeal as a Lithium Alternative
The significance of this research extends beyond the material itself. Interest in sodium-ion batteries has grown rapidly as governments and industries seek alternatives to lithium-based technologies.
Lithium-ion batteries currently dominate energy storage markets, but concerns remain regarding raw material availability, cost volatility, and supply chain security.4
Sodium presents an attractive alternative because it is one of the most abundant elements on Earth. It can be sourced from common salts and is widely distributed geographically, reducing dependence on restricted mineral resources. While sodium-ion batteries generally exhibit lower energy density than their lithium counterparts, ongoing materials innovations continue to narrow this performance gap.4,5
Commandeur et al. (2025) highlight how relatively simple modifications to material structure can unlock higher capacity and faster ionic transport.1 The researchers improved battery performance not through expensive material modifications, but by controlling hydrothermal synthesis conditions and maintaining structural water. This simplicity may benefit future scaling and commercialization efforts.
A Balance Between Capacity and Stability
Interestingly, the study does not suggest that more water is always better. The researchers observed that materials with excessive water content eventually suffered compromised performance, while fully dehydrated materials exhibited lower capacities and poorer ionic transport. The optimal material balanced sodium levels and precisely controlled crystalline water content.1
This nuanced outcome shows that material performance often depends on achieving an optimal structural balance rather than maximizing a single variable. Water increases interlayer spacing and facilitates sodium storage, but too much water clogs diffusion paths and affects long-term performance. Consequently, controlling water rather than eliminating it becomes the critical design strategy.
Such findings reinforce the importance of understanding structure-property relationships at the atomic scale. They also suggest that other battery materials currently subjected to aggressive drying processes may warrant re-examination, particularly if structural water contributes positively to ion transport or storage mechanisms.
Beyond Batteries: A Role in Water Desalination
The Surrey research project stands out because the same material demonstrates promise in applications beyond energy storage. When tested in saline solutions, NVOH functioned as an effective sodium-capturing electrode for electrochemical desalination applications.
Desalination batteries remove sodium and chloride ions from water during charging, reducing salinity while simultaneously storing energy.
The researchers estimated a desalination capacity of 173 mg NaCl per gram, surpassing many previously reported desalination electrode materials.1 The material maintained significant electrochemical activity through 1,000 cycles, highlighting its potential durability in water-treatment environments.
This dual functionality is useful for water treatment given increasing global concerns surrounding water security. Climate change, population growth, and industrial demand are placing mounting pressure on freshwater resources worldwide. Technologies that integrate energy storage and water purification could address two critical sustainability challenges simultaneously.1,6
Redefining Materials Design
This study shows that water inside electrode materials alters ionic conductivity and stability. Scientists should reconsider routine drying because trapped water can affect electrode performance. It highlights the importance of challenging long-held assumptions that can become deeply embedded in scientific thinking.
For years, water removal has been considered a routine and often necessary step in preparing battery electrodes. Surrey researchers found that retaining structural water stabilizes layered frameworks and improves sodium-ion storage capacity.
As sodium-ion technology continues to evolve, breakthroughs may increasingly surface from rethinking established design rules rather than merely searching for entirely new materials.
The discovery that crystalline water can act as a beneficial structural feature highlights the sophistication of modern materials science and the importance of understanding how atomic-scale arrangements influence device performance.
Ultimately, the work highlights the importance of revisiting established assumptions, showing that characteristics once regarded as undesirable may in fact hold the key to improved performance.
References and Further Reading
- Commandeur, D., et. al (2025). Nanostructured sodium vanadate hydrate as a versatile sodium ion cathode material for use in organic media and for aqueous desalination. Journal of Materials Chemistry A, 13, 34493-34506. https://doi.org/10.1039/d5ta05128b
- Deng, C., et. al. (2014). 1D nanostructured sodium vanadium oxide as a novel anode material for aqueous sodium ion batteries. Nano Energy, 4, 49-55. https://doi.org/10.1016/j.nanoen.2013.12.014
- Han, J., et. al. (2024). Layered Structure Modification of Sodium Vanadate through Ca/F Co-Doping for Enhanced Energy Storage Performance. Advanced Energy Materials, 14, (45), 2401481. https://doi.org/10.1002/aenm.202401481
- He, J., et. al. (2024). Tuning the solvation structure with salts for stable sodium-metal batteries. Nature Energy, 9, 446-456. https://doi.org/10.1038/s41560-024-01469-y
- Roberts, S., & Kendrick, E. (2018). The re-emergence of sodium ion batteries: testing, processing, and manufacturability. Nanotechnology, Science and Applications, 11, 23-33. https://doi.org/10.2147/NSA.S146365
- Bevacqua, E., et. al. (2024). Direct and lagged climate change effects intensified the 2022 European drought. Nature Geoscience, 17, 1100-1107. https://doi.org/10.1038/s41561-024-01559-2
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