Sodium metal batteries (SMBs) currently suffer from critical safety and stability issues. To resolve them, researchers have now developed a new polymerisable deep eutectic solvent electrolyte that is not only non-flammable and leakage proof but also enhances long-term stability of SMBs. The electrolyte also allows the battery to be folded or cut, while still delivering consistent power. This electrolyte design can contribute to the development of practical SMBs.
In recent years, sodium-metal batteries (SMBs) are gaining increasing attention for next-generation energy storage technologies due to the abundance and low-cost of sodium (Na) reserves, making them cost-effective alternatives to the current commercial lithium-ion batteries. However, the practical applications of SMBs are still limited by critical safety and stability issues.
SMBs face challenges such as the high reactivity of sodium metal, dendrite growth, and unwanted side reactions, all of which can shorten battery life. When deployed at scale in energy storage systems, high operating temperatures can cause catastrophic failure. In addition, conventional organic liquid electrolytes are volatile, highly flammable, toxic, adding to safety and environmental concerns.
Now, a research team led by Professor Chan-Jin Park from the Department of Materials Science and Engineering at Chonnam National University in South Korea, have developed a new polymerisable deep eutectic solvent (PDES) electrolyte that can address these challenges.
“Our electrolyte combines efficient Na ion transport with improved safety, leakage resistance and interfacial stability, making it a promising candidate for practical sodium-metal batteries” said Professor Park. The study was made available online on August 02, 2026, and published in Volume 90 of Energy Storage Materials on August 01, 2026.
The proposed PDES electrolyte is composed of sodium perchlorate (NaClO4), N-isopropylacrylamide (NIPAM), and succinonitrile (SN). When mixed these components form a homogenous liquid stabilised by intermolecular interactions, including noncovalent interactions like hydrogen bonding and ion-dipole interactions. This mixture, called a deep eutectic solvent (DES), has attractive properties like non-flammability, chemical and thermal stability. However, as electrolytes they are prone to leakage. To address this, the researchers conducted in-situ polymerisation of the mixture, creating a more robust, leakage-free solid matrix, known as PDES.
The intermolecular interactions within the proposed PDES play an important role in enhancing Na-ion transport and addressing issues of conventional SMB electrolytes. NaClO4 is employed as the Na-ion source owing to the weak coordination between the perchlorate (ClO4-) anion and Na-ion, favourable for salt dissociation. NIPAM, through ion-dipole interactions, promotes Na-ion dissociation, while also generating a robust polymer matrix. Meanwhile, SN offers plasticity and further assistance with the Na ion dissociation. Together, these interactions contribute to a favorable environment for Na-ion transport.
As a result, the optimised PDES composition demonstrated a high ionic conductivity of 1.39 mS cm–1 at 30 ◦C, high Na-ion transference number of 0.58, a wide electrochemical stability window. Importantly, the PDES showed high flame retardance on direct exposure to fire and leakage resistance.
Notably, when tested in full cells the PDES electrolyte formed a robust electrode-electrolyte interface on the cathode during cycling, suppressing parasitic side reactions and irregular Na growth. Consequently, the full cell with optimised PDES electrolyte delivered an initial discharge capacity of 110.2 mAh g-1 at 0.1 C with nearly 99 percent coulombic efficiency. Additionally, it demonstrated long-term cycling stability with 90.4 percent capacity retention over 1000 cycles at a rate of 2 C.
The researchers also fabricated a pouch cell using this electrolyte. Interestingly, it could maintain power supply to an LED even when folded and cut, demonstrating its safety and mechanical robustness.
“Our electrolyte design for SMBs can lead to safer, lower-cost and more sustainable rechargeable batteries” added Professor Park. “In future, such batteries could support renewable energy storage at the grid-level, backup power systems, and also low-cost rechargeable battery systems.”
Overall, this innovative electrolyte design will help develop more safe, long-lasting and cost-effective rechargeable batteries.
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