6 Minutes
Breakthrough: Sodium batteries that work at subzero
A research team led by Y. Shirley Meng at the University of Chicago and collaborators has developed a way to stabilize a high-conductivity sodium solid electrolyte that allows all-solid-state sodium batteries to deliver strong performance at room temperature and even below freezing. This advancement addresses a key limitation of sodium-based solid-state batteries and brings sodium chemistry closer to practical use as a lower-cost, more abundant alternative to lithium.
Scientific background and why it matters
All-solid-state batteries replace flammable liquid electrolytes with solid electrolytes, which improves safety and enables higher energy density designs. Most development to date has focused on lithium because lithium-ion chemistries deliver high ionic conductivity and mature manufacturing routes. However, lithium is expensive, geographically constrained, and environmentally challenging to mine at large scale.
Sodium is an attractive alternative: it is more abundant, less costly, and has a smaller environmental footprint. But sodium-based all-solid-state batteries historically suffer from poor ionic conduction and limited electrochemical performance at practical temperatures and with thick electrodes, limiting their real-world applicability.
How the team achieved stabilization of a metastable phase
The team targeted a metastable crystal structure of sodium hydridoborate, a sodium-containing solid electrolyte. According to first author Sam Oh (A*STAR Institute of Materials Research and Engineering, Singapore, and visiting scholar at Meng’s lab), this metastable form exhibits ionic conductivity at least an order of magnitude higher than previously reported phases and three to four orders of magnitude higher than its precursor.
Thermal processing to lock in high conductivity
Researchers applied a controlled thermal treatment: they heated the metastable precursor to the onset of crystallization and then rapidly cooled it. This kinetic stabilization — a well-established technique in materials science — allowed the team to lock in a crystal structure that, while not thermodynamically favored, supports fast sodium-ion transport.
The group then combined this stabilized solid electrolyte with an O3-type layered cathode coated in a chloride-based solid electrolyte. That combination enabled the fabrication of thick, high-areal-loading cathodes instead of the thin cathodes commonly used when ionic conduction is limited.
"The thicker the cathode is, the theoretical energy density of the battery — the amount of energy being held within a specific area — improves," said Sam Oh. Thicker cathodes reduce the proportion of inactive materials and increase the share of active cathode material, improving practical energy per unit area.
New research from the lab of UChicago Pritzker School of Molecular Engineering Liew Family Professor of Molecular Engineering Y. Shirley Meng raises the benchmark for sodium-based all-solid-state batteries as an alternative to lithium-based batteries. Credit: UChicago Pritzker School of Molecular Engineering / Jason Smith
Key results and implications
- Ionic conductivity: The stabilized metastable sodium hydridoborate phase shows dramatically improved sodium-ion conductivity compared with previously reported phases, enabling efficient charge transport through the solid electrolyte at lower temperatures.
- Low-temperature operation: The battery cells with the new electrolyte and thick cathodes maintained performance at room temperature and below freezing — a major step toward practical deployment in temperate and cold climates.
- Manufacturability: Because the stabilization method uses established thermal processing techniques, the approach may be more readily adopted and scaled by industry than entirely novel chemical syntheses.
"It’s not a matter of sodium versus lithium. We need both," said Y. Shirley Meng, Liew Family Professor in Molecular Engineering. "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. This new research gets us closer to that ultimate goal while advancing basic science along the way."
Related technologies and future prospects
This work intersects several active research directions: solid electrolyte discovery, electrode interfaces, and scalable thermal processing. The use of chloride coatings on the O3 cathode improves interfacial compatibility, while the stabilized electrolyte permits higher areal loadings that approach energy densities needed for electric vehicle and grid storage applications.
Remaining challenges include long-term cycling stability, full-cell optimization, and scaling the thermal stabilization process while ensuring reproducible microstructure and phase purity. Nonetheless, because the processing leverages familiar materials-engineering techniques, the pathway to pilot-scale production is clearer than with some high-risk chemistries.
Expert Insight
"Stabilizing a metastable phase to unlock ionic conductivity is a clever and practical route," says Dr. Elena Kim, a solid-state battery researcher (fictional). "If the team can demonstrate consistent long-term cycling and maintain mechanical integrity with thicker electrodes, this could be a pivotal step toward sodium-based systems that compete with lithium in cost-sensitive applications like grid storage."
Conclusion
The University of Chicago-led study shows a pragmatic path to high-performance sodium all-solid-state batteries by kinetically stabilizing a high-conductivity metastable sodium hydridoborate phase and integrating it with thick, chloride-coated O3 cathodes. The result narrows the performance gap between sodium and lithium systems, advancing a more abundant and sustainable option for future energy storage. Continued work on durability, manufacturing scale-up, and full-cell optimization will determine how quickly sodium solid-state batteries move from lab demonstrations to commercial products.
Source: scitechdaily
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