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_12O1FSI) 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_12O1FSI. 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.