Polyethylene Oxide/Sodium Sulfonamide Polymethacrylate Blends as Highly Conducting Single-Ion Solid Polymer Electrolytes

In this work, blends of polyethylene oxide (PEO) and poly(sodium 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethanesulfonyl) imide) (PNaMTFSI) in different compositions were investigated for their application as solid electrolytes for sodium batteries. PNaMTFSI and PEO are miscible, exhibiting only one Tg in the whole range of compositions. PNaMTFSI was shown to reduce the crystal growth rate of PEO crystals but increase PEO nucleation, making the overall crystallization rate higher in blends with 15 and 30 wt % PNaMTFSI. The ionic conductivity is also affected by the blend composition. The highest values of ionic conductivity were observed with 15 and 30 wt % PNaMTFSI at high temperatures equal to 5.84 × 10–5 and 7.74 × 10–5 S cm–1 at 85 °C, respectively, with values of sodium-ion transference numbers of higher than 0.83 and electrochemical stability between 3.5 and 4.5 V versus Na+/Na0 depending on the composition, which opens the possibility of its use in sodium batteries. Finally, a comparison was made between the effect of sodium and lithium on these types of electrolytes, showing that sodium electrolytes have a lower ionic conductivity due to the larger size of the Na cation. The differences in the spherulitic growth rate and overall crystallization rate between Li and Na-containing electrolytes were compared and rationalized in terms of the blends’ intermolecular interactions and the relative contribution of primary nucleation and growth.