How Polymer Influences the Electrochemical Behavior of Eutectogels for Lithium Batteries

Solid electrolytes are regarded as good alternatives for liquid carbonate-based electrolytes, as they show much better safety. In polymeric eutectogel (P-ETG) hybrid solid-state electrolytes, a deep eutectic solvent (DES) is enclosed within a polymer host. They are promising for application in high-energy-density lithium-ion batteries (LIBs) due to their relatively high ionic conductivity at room temperature, compatibility with high-potential positive electrode materials, and improved safety compared to conventional electrolytes. After all, they are less prone to leakage and are potentially nonflammable. Further, they can be obtained through a facile synthesis method, i.e., by ultraviolet (UV) curing. In this work, we study in great detail how the DES–polymer interaction depends on the relative amounts and on the nature of the polymer. The ionic conductivity of the P-ETGs depends on the monomer and cross-linker, reaching values from 0.400 up to 1.011 mS cm –1 at 25 °C. The choice of cross-linker has a significant effect on the ionic conductivity as amides result in less mobile chains compared to esters due to increased rotational barriers. Furthermore, we also study the compatibility with the electrodes, their performance in Li | NMC622 cells, and the correlation with the chemical structure of the polymer. Therefore, the P-ETG electrolyte is an interesting electrolyte for solid-state batteries due to their low cost, flexibility, and compatibility with NMC622 positive electrode materials.