Sodium batteries promise cheap, abundant energy storage free of lithium's supply constraints, but high-voltage versions have faced a chemical dilemma: the sodium metal anode and the high-voltage cathode demand opposite conditions from the electrolyte, and additives that protect one usually degrade the other. Researchers at KAUST's Center of Excellence for Renewable Energy and Storage Technologies, led by Husam Alshareef with lead author Dong Guo, report a way to satisfy both at once.
Their solution, published in Joule, is a class of non-solvating additives. The team chose a fluorinated ether, TTE, that binds weakly to sodium ions and preferentially associates with anions. Rather than following sodium to the anode and decomposing there, it travels with the anions to the cathode and builds a protective layer, a mechanism the authors call anti-solvation. Only about 3 per cent by weight of the electrolyte is needed.
The numbers are compelling: cells retained 90 per cent of capacity after 1,200 cycles, the sodium anode reached a coulombic efficiency of 99.92 per cent, and ampere-hour-scale pouch cells achieved energy densities around 180 watt-hours per kilogram, comparable to lithium iron phosphate. Because the additive drops into standard ether electrolytes using commercially available chemicals, the route is compatible with existing manufacturing, targeting grid storage, backup power and cost-sensitive electric vehicles.