Sodium-based battery design maintains performance at room and subzero temperatures

All-solid-state batteries are safe, powerful ways to power EVs and electronics and store electricity from the energy grid, but the lithium used to build them is rare, expensive and can be environmentally devastating to extract.

Sodium is an inexpensive, plentiful, less-destructive alternative, but the all-solid-state batteries they create currently don’t work as well at room temperature.

“It’s not a matter of sodium versus lithium. We need both. When we think about tomorrow’s energy storage solutions, we should imagine the same gigafactory can produce products based on both lithium and sodium chemistries,” said Y. Shirley Meng, Liew Family Professor in Molecular Engineering at the UChicago Pritzker School of Molecular Engineering (UChicago PME). “This new research gets us closer to that ultimate goal while advancing basic science along the way.”

A paper from Meng’s lab, published this week in Joule, helps rectify that problem. Their research raises the benchmark for sodium-based all-solid-state batteries, demonstrating thick cathodes that retain performance at room temperature down to subzero conditions.

The research helps put sodium on a more equal playing field with lithium for electrochemical performance, said first author Sam Oh of the A*STAR Institute of Materials Research and Engineering in Singapore, a visiting scholar at Meng’s Laboratory for Energy Storage and Conversion during the research.

How they accomplished that goal represents an advance in pure science.

“The breakthrough that we have is that we are actually stabilizing a metastable structure that has not been reported,” Oh said. “This metastable structure of sodium hydridoborate has a very high ionic conductivity, at least one order of magnitude higher than the one reported in the literature, and three to four orders of magnitude higher than the precursor itself.”

Established technique, new field

The team heated a metastable form of sodium hydridoborate up to the point it starts to crystallize, then rapidly cooled it to kinetically stabilize the crystal structure. It’s a well-established technique, but one that has not previously been applied to solid electrolytes, Oh said.

That familiarity could, down the road, help turn this lab innovation into a real-world product.

“Since this technique is established, we are better able to scale up in the future,” Oh said. “If you are proposing something new or if there’s a need to change or establish processes, then industry will be more reluctant to accept it.”

Pairing that metastable phase with an O₃-type cathode that has been coated with a chloride-based solid electrolyte can create thick, high-areal-loading cathodes that put this new design beyond previous sodium batteries. Unlike design strategies with a thin cathode, this thick cathode would pack less of the inactive materials and more cathode “meat.”

“The thicker the cathode is, the theoretical energy density of the battery—the amount of energy being held within a specific area—improves,” Oh said.

The current research advances sodium as a viable alternative for batteries, a vital step to combat the rarity and environmental damage of lithium. It’s one of many steps ahead.

“It’s still a long journey, but what we have done with this research will help open up this opportunity,” Oh said.