Cationic polymer-in-salt electrolytes for fast metal ion conduction and solid-state battery applications

Polymer electrolytes provide a safe solution for future solid-state high-energy-density batteries. Materials that meet the simultaneous requirement of high ionic conductivity and high transference number remain a challenge, in particular for new battery chemistries beyond lithium such as Na, K and Mg. Herein, we demonstrate the versatility of a polymeric ionic liquid (PolyIL) as a polymer solvent to achieve this goal for both Na and K. Using molecular simulations, we predict and elucidate fast alkali metal ion transport in PolyILs through a structural diffusion mechanism in a polymer-in-salt environment, facilitating a high metal ion transference number simultaneously. Experimental validation of these computationally designed Na and K polymer electrolytes shows good ionic conductivities up to 1.0 x 10(-3) S cm(-1) at 80 degrees C and a Na+ transference number of similar to 0.57. An electrochemical cycling test on a Na divide 2:1 NaFSI/PolyIL divide Na symmetric cell also demonstrates an overpotential of 100 mV at a current density of 0.5 mA cm(-2) and stable long-term Na plating/stripping performance of more than 100 hours. PolyIL-based polymer-in-salt strategies for new solid-state electrolytes thus offer an alternative route to design high-performance next-generation sustainable battery chemistries.

Automated summary

Polymer electrolytes are important for future high-energy-density batteries. In this study, a polymeric ionic liquid was used as a polymer solvent to achieve high ionic conductivity and metal ion transference number simultaneously for sodium and potassium electrolytes. Experimental results confirmed the predicted fast ion transport in the polymer-in-salt environment, and demonstrated good ionic conductivity and stable cycling performance. This research offers an alternative strategy for designing high-performance sustainable battery chemistries.