Electrolyte Technologies for Sodium-Based Energy Storage Systems

Electrolytes lie at the heart of sodium-based energy storage, mediating ion transport, interfacial stability and safety. Conventional liquid electrolytes employ sodium salts (for example, NaPF6, NaTFSI or NaFSI) dissolved in carbonate or ether solvents, with additives introduced to tailor the solvation structure and form a robust solid electrolyte interphase (SEI). Advances in nonflammable media such as deep eutectic solvents and flame-retardant sulfolane blends address safety and high-voltage operation, while polymer and quasi-solid-state formulations improve mechanical integrity, suppress dendrite growth and enable operation over a wide temperature range. Ceramic solid electrolytes such as Na-β″-alumina offer high ionic conductivity and chemical stability but require careful interfacial engineering to lower resistance. Across all systems, control of ion coordination and interphase chemistry underpins improvements in cycle life, rate capability and temperature tolerance, unlocking grid-scale and stationary storage applications alongside emerging low-temperature and fast-charging scenarios.

Research from Nature Portfolio

Recent studies have demonstrated specific ether-based electrolyte formulations that maintain fluidity and form stable SEI layers down to –80 °C, enabling long-term cycling of sodium metal cells at subzero conditions. Detailed ex situ spectroscopy and microscopy have revealed the role of mixed linear and cyclic ethers in reducing electrolyte resistance and guiding SEI composition to suppress dendrite initiation. In another seminal work on sodium–nickel chloride systems, an intermediate-temperature architecture (190 °C) achieved ultra-high energy density by decelerating cathode particle growth and optimising molten‐salt transport, thereby extending cycle life to over 1,000 cycles. These breakthroughs highlight the importance of tailored solvent-salt interactions and temperature-dependent interfacial phenomena in advancing both low- and intermediate-temperature sodium technologies.

Research from all publishers

A nonflammable sulfolane–NaTFSI blend with fluoroethylene carbonate additive has been shown to generate a dense, heteroatom-rich cathode–electrolyte interphase on high-voltage NaNMF cathodes, achieving over 80 % capacity retention at 4.2 V for 400 cycles. Parallel work on sodium bis(fluorosulfonyl)imide in triethyl phosphate has delivered stable cycling of Na||NaNi0.68Mn0.22Co0.10O2 cells at 4.2 V, with minimal transition-metal dissolution and 89 % retention after 500 cycles. Deep eutectic solvents based on NaTFSI and N-methyl acetamide provide high anodic stability (up to 4.65 V vs. Na/Na+), enhanced film formation at the electrode interface and over 97 % capacity retention at elevated temperatures. Collectively, these developments illustrate how innovative salt–solvent chemistries and nonvolatile media yield safer, high-performance sodium electrochemistries for stationary and emerging applications.

Electrolyte Technologies for Sodium-Based Energy Storage Systems publication trend

The graph below shows the total number of articles in electrolyte technologies for sodium-based energy storage systems across all publications each year (not limited to Nature Index journals).

Technical terms

Solid Electrolyte Interphase (SEI): A passivating layer formed on electrode surfaces that stabilises cycling by preventing continuous electrolyte decomposition and suppressing dendrite growth.

Solvation Structure: The arrangement of solvent molecules and anions around a sodium ion, which governs transport kinetics, interphase chemistry and electrochemical stability.

Quasi-Solid-State Electrolyte: A hybrid medium combining polymer or gel matrices with liquid components to balance ionic conductivity, mechanical robustness and safety.

Deep Eutectic Solvent (DES): A eutectic mixture of hydrogen-bond donors and acceptors that forms a low-melting, nonflammable ionic medium for enhanced safety and interfacial film formation.

Ionic Conductivity: A measure of the ease with which sodium ions migrate through the electrolyte, critical to power density and rate performance.

References

1. Sulfolane-Based Flame-Retardant Electrolyte for High-Voltage Sodium-Ion Batteries. Nano-Micro Letters (2024).
2. Electrolyte Solvation Structure Design for Sodium Ion Batteries. Advanced Science (2022).
3. Advanced intermediate temperature sodium–nickel chloride batteries with ultra-high energy density. Nature Communications (2016).
4. Extending the low-temperature operation of sodium metal batteries combining linear and cyclic ether-based electrolyte solutions. Nature Communications (2022).
5. Deep Eutectic Solvents as Nonflammable Electrolytes for Durable Sodium‐Ion Batteries. Advanced Energy and Sustainability Research (2022).