Gel polymer electrolytes based on sulfonamide functional polymer nanoparticles for sodium metal batteries

In this work, we investigate the development of polymer electrolytes for sodium batteries based on sulfonamide functional polymer nanoparticles (NaNPs). The synthesis of the polymer NaNPs is carried out by emulsion copolymerization of methyl methacrylate and sodium sulfonamide methacrylate in the presence of a crosslinker, resulting in particle sizes of 50 nm, as shown by electron microscopy. Then, gel polymer electrolytes are prepared by mixing polymer NPs and different organic plasticizers including carbonates, glymes, sulfolanes and ionic liquids. The chemical nature of the plasticizer resulted in different effects on the sodium coordination shell, which in turn impacted the properties of each membrane as investigated by FTIR. The transport properties were investigated by EIS and solid-state NMR. Among the organic gel polymer electrolytes (GPEs), the system comprising NaNPs and sulfolanes achieved the best ionic conductivity (1.1 × 10^-4 S cm^-1 at 50 °C) and sodium single-ion properties while for the ionogels, the best ionic conductivity was obtained by NaNPs mixed with pyrrolidinium-FSI IL (4.7 × 10^-4 S cm^-1 at 50 °C). From sodium metal symmetrical cell cycling, the use of ILs as plasticizers proved to be more beneficial for SEI formation and its evolution during cell cycling compared to the systems based on NPs and organic solvents. However, NPs + PC led to lower cell overvoltage than NPs + ILs (<0.4 V vs. >0.5 V). This study shows the potential of using Na-sulfonamide functional polymer nanoparticles to immobilize different plasticizers and thereby obtain soft-solid electrolytes for Na metal batteries.