en.Wedoany.com Reported - A research team led by Associate Professor Palani Balaya from the Department of Mechanical Engineering at the National University of Singapore's College of Design and Engineering has successfully addressed key challenges in the safety and performance of all-solid-state sodium batteries by using a low-cost graphitic carbon nitride (GCN) additive. This achievement provides a scalable pathway toward safe and economical all-solid-state sodium batteries, with the findings published in the journal Advanced Functional Materials.
The uneven global distribution of lithium resources and rising costs have driven the industry to seek alternatives. Sodium is approximately 1,000 times more abundant in the Earth's crust than lithium and can be extracted from seawater, making it an ideal candidate for grid-scale energy storage. However, most sodium-ion batteries rely on flammable liquid electrolytes, posing safety risks. Solid polymer electrolytes can eliminate these hazards, but they suffer from slow sodium-ion conduction and unstable contact with sodium metal anodes, leading to dendrite formation and short circuits.
The research team incorporated GCN into polymer electrolyte films made from polyethylene oxide and sodium salts. GCN is a nitrogen-rich material synthesized by heating urea in air to 550 degrees Celsius, forming flakes about two nanometers thick. The high specific surface area of GCN disrupts the polymer's tendency to form rigid crystalline regions, promoting the formation of flexible disordered regions that allow sodium ions to move more freely. Additionally, the nitrogen-rich active sites on its surface pull sodium ions away from their corresponding sodium salts, releasing more charge carriers. This combined effect more than doubles the ionic conductivity of the electrolyte at 55 degrees Celsius and increases the transference number from 0.19 to 0.51, reducing polarization and enhancing efficiency.
The GCN additive also alters the interface between the electrolyte and the sodium metal electrode. The composite polymer is three times stronger than the unmodified polymer, physically preventing dendrite penetration. At the same time, the additive promotes the formation of an inorganic-rich sodium-based protective layer on the electrode surface, guiding uniform sodium deposition and suppressing side reactions. At a current density of 0.1 mA cm⁻², the modified electrolyte operated stably for 1,000 hours without short-circuiting, whereas the unmodified electrolyte short-circuited within 250 hours. At a current density of 0.2 mA cm⁻², the modified electrolyte operated for over 2,000 hours without failure.
The research team assembled all-solid-state batteries using carbon-coated zinc-doped sodium vanadium phosphate cathodes and sodium metal anodes for evaluation. At a charge-discharge rate of 0.5C, the battery retained 95% capacity after 500 cycles with a Coulombic efficiency of approximately 99.97%, and could withstand rates up to 2C, recovering 99% of capacity upon returning to lower rates. The researchers also constructed a single-layer pouch cell that continued to power a light-emitting diode during folding, unfolding, and even cutting, without short-circuiting.
This all-solid-state system is the latest achievement of the sodium-ion battery research project at the National University of Singapore's College of Design and Engineering. The team has also developed non-flammable liquid electrolytes that can withstand direct flame contact for 60 seconds and remain stable at temperatures up to 270 degrees Celsius, as well as flame-retardant electrolytes and moisture-resistant layered oxide cathodes. Currently, the team is optimizing solid-state sodium-ion batteries for stable operation near room temperature, aiming for stable performance at 45 degrees Celsius, while developing bipolar all-solid-state architectures to enhance energy density.
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