Infrared studies of polyacrylonitrile-based polymer electrolytes incorporated with lithium bis(trifluoromethane)sulfonimide and urea as deep eutectic solvent

• PAN–DMF–LiTFSI–urea polymer electrolyte film is investigated for the first time.
• Interactions between LiTFSI and urea as DES are studied and differ from choline chloride–urea.
• Urea helps to dissociate LiTFSI and acts as additional ion conduction pathway for lithium cations.

In this work, urea is introduced into polyacrylonitrile (PAN)-based polymer electrolyte containing lithium bis(trifluoromethane)sulfonimide (LiTFSI) to form a deep eutectic solvent with urea and LiTFSI in the mole ratio of 1:3. The ambient ionic conductivity of the polymer electrolyte film is enhanced from 2.54 × 10−4 S cm−1 to 3.82 × 10−3 S cm−1 with the addition of urea. Infrared studies has revealed that urea interacts with the LiTFSI through coordination of Li+ ions onto the carbonyl (CO) group of urea, and hydrogen bonding possibly to the O atoms in the SO2 groups of TFSI− ions. Hydrogen bonding interactions of urea with DMF and PAN are also evident. The enhancement in conductivity is believed to be due to urea being involved in the dissociation of LiTFSI and its role as an additional ion conduction pathway through its carbonyl group.

FTIR deconvolution between 3000 and 3700 cm−1 of (a) urea, (b) DMF–urea, (c) LiTFSI, (d) LiTFSI–urea, and (e) PAN–DMF–LiTFSI–urea.Figure optionsDownload high-quality image (64 K)Download as PowerPoint slide