Tech
Sodium-Sulfur Hits $5/kWh in Raw Materials. No One to Build It.
A January 2026 Nature paper priced sodium-sulfur raw materials at $5.03 per kilowatt-hour, against $70/kWh for a finished stationary-storage pack. The largest commercial sodium-sulfur manufacturer had stopped taking orders two months earlier.
A sodium-sulfur battery from Hao Sun's group at Shanghai Jiao Tong University cleared 3.6 volts at room temperature in a Nature paper dated January 7.
Standard room-temperature sodium-sulfur cells stay below 1.6 volts. The SJTU design uses sulfur tetrachloride as a cathode reaction intermediate, made reversible by sodium dicyanamide in a non-flammable chloroaluminate electrolyte. The electrode delivers 1,198 watt-hours per kilogram. Add a bismuth covalent-organic-framework catalyst and that rises to 2,021 Wh/kg at the electrode level. Commercial lithium-ion cells run 250-300 Wh/kg at the full-cell level; that figure includes electrolyte, separator, and casing mass the electrode number excludes.
The team's raw-material cost estimate is $5.03 per kilowatt-hour. BloombergNEF's December 2025 survey put finished stationary-storage packs at $70/kWh. The team has not published a delivered-cell-cost estimate; neither has any outside lab.
What the Electrolyte Requires
The chemistry that produces 3.6 volts creates the manufacturing problem. Sulfur tetrachloride is corrosive. Handling it at factory scale requires equipment that standard battery plants do not carry.
Kevin Ryan at the University of Limerick told Chemistry World the challenges are "surmountable" and pointed to "real potential for grid-level energy storage." Serena Cussen at University College Dublin called the electrolyte's role "crucial and elegant." Neither comment addressed the capital commitment a factory requires. The cell also degrades in air, meaning assembly demands an inert atmosphere.
No outside lab has published a replication. The SJTU team told Chemistry World small-scale products are possible in three years; commercial products within five.
The Commercial Context
NGK Insulators announced on October 31, 2025, that it was discontinuing NAS battery manufacturing and would stop accepting new orders. The company had deployed more than 5 gigawatt-hours of sodium-sulfur storage globally, the second-largest footprint of any grid storage technology in the world.
BASF, which co-developed the product since 2019, withdrew in September 2025 under CEO Markus Kamieth, redirecting toward core chemical segments. NGK's NAS cells operate at 300 degrees Celsius. The SJTU design runs at room temperature, eliminating the thermal-management burden that made NAS expensive to maintain.
Duke Energy commissioned its 5 MW NAS pilot at the Suwannee River site in Florida on May 22, 2025, five months before NGK stopped taking orders. Duke holds working proof-of-concept hardware with no available supplier for additional units.
BASF's exit names the gap the SJTU paper never addresses: deployable sodium-sulfur chemistry has always required an industrial partner with a 20-year commercial horizon. The SJTU design's reaction pathway is different; the industrial threshold to scale it is the same.
The SJTU team's five-year timeline places a commercial cell at 2031. NGK's NAS chemistry was simpler and required less specialized handling; it still took decades from laboratory demonstration to gigawatt-hour deployment. Watch for a manufacturing license or joint-venture filing before 2028; if neither appears, the $5.03 raw-material advantage stays locked in a fume hood.