Sodium-Ion Battery Electrolyte Optimization

Sodium-ion batteries offer a cost-effective and sustainable alternative to lithium-ion systems, yet their practical deployment hinges on the careful design of the electrolyte. An electrolyte serves both as the ion‐conducting medium and as the source of interphase components that form the solid electrolyte interphase (SEI) on electrode surfaces. Optimising electrolyte composition—by selecting appropriate salts, solvents and additives—can markedly improve ionic conductivity, interfacial stability, rate capability and cycle life. Ether-based systems often afford lower viscosity and enhanced solvation dynamics, whereas carbonate solvents provide a broad electrochemical window but may yield thicker, less stable SEI layers. Tailoring the anion chemistry has emerged as a powerful lever to control SEI composition, suppress dissolution of interphase species and reduce charge-transfer resistance. Additives such as fluorinated compounds can further stabilise interphases by forming robust, inorganic-rich films. Advances in computational modelling and interfacial characterisation are now guiding the rational formulation of next-generation electrolytes that balance high energy density, fast kinetics and safety, enabling sodium-ion battery applications in grid storage, electrified transport and sustainable portable electronics.

Research from Nature Portfolio

Recent studies have shown that coupling titanium dioxide and other anode materials with an ether-based solvent such as diglyme leads to superior efficiency and reversible capacity compared with conventional carbonate systems. Detailed interfacial analyses reveal that differences in sodiation depth induce distinct structural evolution at the electrode–electrolyte boundary. The energy barrier to charge transfer at this interface emerges as the dominant factor governing electrochemical performance, and a new parameter has been proposed to quantify sodiation dynamics. These insights pave the way for the rational design of aprotic electrolytes that achieve both high stability and enhanced sodium storage properties.

Research from all publishers

A recent case study of hard-carbon electrodes in a diglyme solvent compared the impact of NaBF₄, NaPF₆ and NaSO₃CF₃ salts. Density functional theory and electrochemical tests demonstrated that PF₆⁻ preferentially decomposes to form a NaF-rich SEI, yielding faster ionic diffusion, lower interfacial resistance and markedly improved rate capability and cycle life relative to alternative anions. Another investigation quantified capacity losses associated with SEI formation, dissolution and reformation across nine electrolyte formulations. By combining X-ray photoelectron spectroscopy, gas chromatography–mass spectrometry and nuclear magnetic resonance, the work highlighted how the interplay between electrolyte chemistry and SEI thickness governs self-discharge and long-term capacity retention. A further study challenged the prevailing view that ester electrolytes are inherently inferior to ethers, developing a corrected half-cell protocol to eliminate sodium-electrode interference. This revealed that, in full-cell configurations, ester and ether systems exhibit comparable rate performance and underscored the necessity of standardised testing protocols for reliable assessment.

Sodium-Ion Battery Electrolyte Optimization publication trend

The graph below shows the total number of articles in sodium-ion battery electrolyte optimization across all publications each year (not limited to Nature Index journals).

Technical terms

Electrolyte: Ionic conductor composed of dissolved salts and solvents that facilitates ion transport between electrodes.

Solid electrolyte interphase (SEI): Thin film formed on anode surfaces by electrolyte decomposition that regulates ion flow and protects the electrode.

Ether-based electrolyte: Electrolyte that uses ether solvents, offering low viscosity and improved interfacial compatibility.

Carbonate-based electrolyte: Electrolyte that uses carbonate solvents, typically offering wide electrochemical stability but higher viscosity.

Anion: Negatively charged ion of the dissolved salt which influences solvation structure and interphase composition.

References

1. Electrolytes and Interphases in Sodium‐Based Rechargeable Batteries: Recent Advances and Perspectives. Advanced Energy Materials (2020).
2. Evolution of the electrochemical interface in sodium ion batteries with ether electrolytes. Nature Communications (2019).
3. The effect of salt anion in ether‐based electrolyte for electrochemical performance of sodium‐ion batteries: A case study of hard carbon. Carbon Energy (2024).
4. Fundamental Understanding and Quantification of Capacity Losses Involving the Negative Electrode in Sodium‐Ion Batteries. Advanced Science (2023).
5. Revisiting Electrolyte Kinetics Differences in Sodium Ion Battery: Are Esters Really Inferior to Ethers?. Energy & Environmental Materials (2022).