Researchers from Bournemouth University, Sheffield Hallam University and Birmingham City University in the United Kingdom have developed a new type of gel polymer electrolyte with a dual additive system that could significantly improve the performance of promising sodium-metal batteries. These batteries are seen as a cheaper and environmentally sustainable alternative to lithium-ion batteries, since sodium is abundant in nature and is not considered a critically scarce element.
The widespread adoption of sodium-metal batteries continues to face a few fundamental challenges: a tendency to form dangerous dendrites (needle-like metal growths that cause short circuits), comparatively low ionic conductivity and unstable operation at high currents. The British researchers suggest that these limitations could be overcome by fine-tuning the electrolyte so that it not only efficiently conducts sodium ions but also forms a strong and stable protective layer on the electrode surface.
To achieve this, they created a composite material based on a polymer matrix with two key additives: potassium tetrafluoroborate and lithium difluoro(oxalato)borate. The first additive, which contains fluorine, promotes the formation of an inorganic layer rich in sodium fluoride on the surface of the sodium anode, which effectively inhibits dendrite growth. The second additive, which is borate-based, enhances the mechanical strength of this protective layer while increasing its ionic conductivity. The combined action of these components produces a pronounced synergistic effect, which cannot be achieved with either additive individually.
The researchers then built a detailed mathematical model that describes the behavior of the electrolyte and the entire battery in various operating modes with high accuracy. The modeling included calculations of ionic migration, electrochemical reaction kinetics and protective interfacial layer growth, as well as an assessment of the system’s resistance to dendrite formation.
The results were encouraging. Calculations show that the new gel electrolyte exhibits ionic conductivity at room temperature that is about 20% higher than that of standard gel equivalents. Its electrochemical stability window reaches approximately 5 V, opening the possibility of working with higher-voltage cathode materials. Especially impressive are the service life predictions: the model showed that a symmetrical cell with sodium electrodes can reliably operate for over 1,200 hours without signs of degradation caused by dendrites, and a fully functional battery with a sodium vanadium phosphate cathode retains some 93% of its initial capacity even after the equivalent of 7,000 fast charge and discharge cycles.
The researchers hope that these calculated results will help accelerate the development and implementation of next-generation sodium metal batteries, especially in storage systems for power grids, solar power plants and wind farms.
