Scientists from Portugal’s University of Minho and Spain’s University of the Basque Country have developed a method for producing solid polymer electrolytes for lithium-ion batteries with the use of 3D printing. Their paper proves that the replacement of conventional toxic solvents with more environmentally friendly alternatives has a direct impact on the material’s properties and battery performance.
It is widely known that modern lithium-ion batteries use liquid electrolytes, which ensure the transfer of lithium ions between electrodes. Despite their high efficiency, these systems are associated with risks, since liquid components can be toxic and flammable. Solid electrolytes, including polymers combining mechanical strength with the ability to conduct ions, are being considered as an alternative.
In their study, the scientists used a fluorinated polymer supplemented with an ionic liquid to enhance conductivity and a zeolite to stabilize the material’s structure. The key technological solution was the use of direct extrusion, which allows the user to shape the electrolyte into specific structures with high precision. This approach improves contact between battery components and makes it possible to control battery geometry.
The researchers paid particular attention to the choice of solvent used in the printing mixture. Although toxic dimethylformamide is typically used, the scientists replaced it with safer substances: acetone, dimethyl sulfoxide and N-methyl-2-pyrrolidone. They found that the solvent largely determines the material’s structure, strength and ability to conduct lithium ions.
The best results were demonstrated by acetone. Due to its low boiling point, it evaporates quickly during the printing process, facilitating the formation of a more ordered structure. The resulting electrolyte showed the highest ionic conductivity at about 1.5 × 10⁻⁵ S/cm. This means significantly faster and more efficient movement of lithium ions within the material, leading to more stable battery performance.
Tests of assembled solid-state cells confirmed these conclusions. Batteries with electrolyte produced using acetone retained some 90% of their capacity after 60 charge-discharge cycles and achieved a specific capacity of 135 mAh per gram. Samples with other solvents performed worse, partly due to a less stable structure and poorer contact within the battery.
