Developing a novel polyurethane-based gel polymer electrolyte to enable high safety and remarkably cycling performance of sodium ion batteries

A novel gel polymer electrolyte (GPE) with polydopamine (PDA) modified thermoplastic polyurethane (TPU) porous membranes as the matrix skeleton and N-methyl-N-methoxyethyl pyrrolidine bis (fluorosulfonyl) imine (Pyr 12O1 FSI) ionic liquid (IL) as the plasticizer is successfully demonstrated to be suitable for sodium ion batteries (SIBs). The GPE exhibits excellent heat resistance due to the non-flammability of Pyr 12O1 FSI. Moreover, Density Functional Theory (DFT) and Fourier transform infrared spectroscopy (FTIR) results indicate that there is a strong intermolecular interaction between PDA, TPU and IL, thus greatly improving the structural stability and mechanical properties of this GPE. In addition, the functional groups (-OH and –NH–) in PDA have strong hydrogen bonds with TFSI − in sodium bis (trifluoromethanesulfonyl) imide (NaTFSI), which can immobilize TFSI − anions and promote Na + selective transport. Therefore, the ionic conductivity and Na + transference number of the GPE-based SIBs are significantly increased to 3.57 × 10 −4  S cm −1 and 0.34 at 30 °C. As a consequence, Na|TPU@PDA-IL GPE|Na symmetric cells exhibit an ultra-long cycle life for 1200 h at 0.1 mA cm −2 . This work provides an approach to develop GPE for high safety and excellent electrochemical performance SIBs.