The work, led by Professor Husam Alshareef and due to be published in Joule, introduces fluorinated ether NSAs such as 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) as a way to stabilise anode and cathode surfaces in sodium cells.
Prof Alshareef explained that NSAs differ from conventional electrolyte additives in how they interact with species inside the cell. Conventional additives are ‘strongly solvating’ and bind tightly to sodium cations. He said that during charging, the cations move toward the sodium metal anode and drag these additives along with them, leaving the positive cathode exposed and unprotected just when it is most vulnerable to high-voltage oxidation. He added that these additives often decompose aggressively once they reach the sodium metal anode, causing corrosion.
By contrast, the KAUST team’s NSAs do the opposite, said Prof Alshareef.
“They barely interact with the sodium ions at all. Instead, they selectively bind to the negative anions. Since anions move toward the positive cathode during charging, they effectively ‘ferry’ our additive exactly where it is needed most. This creates a robust, protective interphase on the cathode that prevents the electrolyte from breaking down at high voltages [4.3V].”
Test data indicate that the approach stabilises both electrodes under cycling and storage. On the anode side, Alshareef reported that the anti-solvation mechanism allowed sodium metal to retain nearly perfect efficiency (~99.9 per cent) over hundreds of cycles, limiting loss of active sodium and electrolyte.
On the cathode side, fully charged cells stored at 4.3V for 60 days recovered 90 per cent of their capacity, which he said shows that the NSA-based electrolyte does not just slowly degrade over time, even when idle at full charge.
The formulation has been demonstrated beyond coin cells. “We have successfully tested this electrolyte formulation in larger, Ah-level pouch cells,” said Alshareef, citing energy densities around 180Wh kg⁻¹ in soft-pack formats relevant to industrial evaluation.
On scalability and sourcing, Prof Alshareef said the design aims to avoid bottlenecks seen in other advanced electrolytes such as localised high-concentration systems that require large amounts of fluorinated diluents, often exceeding 50 per cent of the total electrolyte weight.
He added that the KAUST electrolyte uses standard, low-cost ether electrolytes with only a trace amount (three per cent by weight) of the NSA additive. TTE is commercially available and used in other industrial applications, and because only small quantities are needed, the cost impact is negligible, and there are no special processing requirements for battery manufacturers.
“They can use their existing injection lines,” he said.
Prof Alshareef identified stationary grid storage and low- to mid-range electric vehicles as the first viable targets for the technology.
“For these applications, the absolute highest energy density is often less critical than cost, cycle life, and the use of abundant materials. Our technology excels here.” He noted that sodium costs less than one per cent of what lithium costs to mine and refine and said the team is achieving cycle life and stability that rivals or even exceeds many lithium-ion systems, especially under high-voltage stress.
By enabling high-voltage cathodes such as Na₃V₂(PO₄)₂F₃, the group is reaching energy densities comparable to lithium iron phosphate (LFP), the current standard for standard-range Teslas and grid storage, and also sees potential in solar-powered desalination plants.