Sodium-ion battery storage for ultra-low temperatures

A research group led by scientists from Purdue University has fabricated a sodium-ion battery (SIB) pouch cell using components compatible with extremely low temperatures and tested it under harsh conditions while connected to renewable energy sources. SIB technology is considered a more sustainable alternative to conventional lithium-ion batteries, as sodium compounds are more abundant.

“Our research presents the first practical evaluation and field demonstration of a sodium-ion pouch cell battery operating at ultra-low temperatures, proving its stability for wind and solar energy storage down to -100 C,” corresponding author Vilas G. Pol told pv magazine. “By employing a commercial-like pouch cell assembly and demonstrating performance in extreme conditions, the work paves the way for the deployment of sustainable battery energy storage systems in harsh climates and space applications.”

The SIB anode consisted of hard carbon (HC) with 90% active material, while the cathode was made of sodium vanadium phosphate, Na₃V₂(PO₄)₃ (NVP), with 85% active material. Multiple layers of these were stacked with a polypropylene separator (Celgard 2500) and secured with adhesive tape. Aluminum tabs were welded to the electrodes, and the stack was enclosed in a polymer-coated aluminum pouch. After sealing three sides, the researchers filled the open side with electrolyte inside an argon-filled glove box. The electrolyte was a 1 M solution of NaPF₆ in a 1:1 mixture of tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF).

For laboratory tests, the team built an extremely low-temperature system (ELTS) cooled with liquid nitrogen (LN₂). A temperature controller regulated the LN₂ flow to maintain the cooling plate temperature. Argon gas was used to purge moisture, and the system was wrapped and filled with Fiberfrax for additional insulation. The tests included electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge (GCD) measurements.

In initial evaluations, the SIB pouch cells were cycled between 2.5 and 3.8 V at room temperature (25°C), –25°C, and –50°C. The specific energy achieved was approximately 96 Wh/kg at room temperature, 74 Wh/kg at –25 C, and 46 Wh/kg at –50 C. In another laboratory setup, the team connected the SIB to a small windmill generator to simulate renewable generation, with a table fan providing airflow. Under these conditions, the cell delivered 85 Wh/kg, 47 Wh/kg, and 39 Wh/kg at room temperature, –25 C, and –50 C, respectively.

The researchers also tested the windmill–battery setup outdoors in West Lafayette, Indiana, where temperatures were around –10°C. “It supports our laboratory measurements of the charging-discharging performance of SIB at very low temperature,” the group reported. In a final experiment, they returned to the lab to operate the SIB at –100°C while coupling it with a polycrystalline silicon solar cell, under conditions similar to those encountered in space environments. In this setup, the SIB achieved specific energy values of up to 76 Wh/kg.

“The study showed that when deployed for solar energy storage, the sodium-ion pouch cell retained remarkable stability and delivered a specific energy of approximately 70 Wh/kg at this extremely challenging temperature—an essential capability for applications such as deep-space missions or very harsh, cold climates,” Pol said. “Balancing the voltage–current dynamics between the solar cell—whose efficiency increases as the silicon band gap widens in the cold—and the battery at low temperatures is a significant challenge, but the students succeeded in doing so effectively.”

Pol added that the team is already exploring other solar-cell-and-battery combinations suitable for extreme environments. “We’ve already performed further activities on different solar cells and coupling with other types of batteries. This follow-up research expands the scope of our initial findings by investigating new pairings, such as high-efficiency perovskite solar cells coupled with other sustainable battery chemistries,” he said.

Their findings were published in “Evaluating sodium-ion pouch cell battery for renewable energy storage under extreme conditions,” in Communications Chemistry. Aside from scientists from Purdue University, researchers from India’s Council of Scientific & Industrial Research (CSIR) – National Chemical Laboratory (NCL) have participated in the study.