Nature Energy study details sodium‑ion cells that keep working in sub‑zero conditions

Researchers at Pacific Northwest National Laboratory and Contemporary Amperex Technology reported in Nature Energy on Wednesday that laboratory pouch cells using a sodium ion chemistry maintained high capacity at sub zero temperatures with multi thousand cycle life at room temperature. The team says the design targets known barriers to commercialization, in particular sluggish low temperature kinetics and early capacity loss.

The paper lands as automakers and storage developers evaluate lithium alternatives amid price swings and supply risks. CATL began limited sodium ion deployments in 2024, but cold weather performance and energy density have constrained wider rollout.

What the study shows

The group led by Jun Liu and Chongmin Wang at PNNL combined a tailored hard carbon anode with a Prussian white cathode and an ether carbonated electrolyte that includes a fluorinated phosphate additive to stabilize the interphase. In operando X ray diffraction and cryogenic electron microscopy tracked sodium staging in the anode and formation of an inorganic rich solid electrolyte interphase.

Pouch cells reached about 150 watt hours per kilogram at the cell level, retained around 80 percent of capacity after roughly 2,000 cycles at 25 degrees Celsius, and sustained discharge at minus 20 degrees Celsius with modest capacity loss at low rates. The authors report reduced impedance growth relative to baseline electrolytes, and they attribute the improvement to faster sodium transport in enlarged nanochannels within the hard carbon and to a more robust interphase.

The team used presodiation to offset first cycle loss, a known issue for hard carbon based sodium cells. The paper describes a sacrificial salt approach and quantifies coulombic efficiencies in the first ten cycles, but it does not present long term calendar aging data or abuse testing.

Industry context

CATL provided cell fabrication expertise and materials benchmarking, according to the author list and methods. The company has announced plans to pair sodium ion with lithium iron phosphate in entry level vehicles and in stationary storage, where cost and temperature tolerance can matter more than peak energy density.

The work does not close the gap to nickel rich lithium ion cells on energy per kilogram, and the cold weather data reflect low rate operation rather than fast charging. It does provide peer reviewed evidence that sodium ion cells can operate in freezing climates with less performance penalty, which has been a central technical concern for bus fleets and distributed storage projects in northern markets.

If the reported interphase chemistry and presodiation protocol transfer to pilot lines, sodium ion could take a larger share of short range mobility and grid applications, which would diversify battery supply chains and reduce pressure on lithium and graphite procurement.