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 × 10−3 S cm−1 at 80 °C and a Na+ transference number of ~0.57. An electrochemical cycling test on a Na∣2:1 NaFSI/PolyIL∣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.
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F.C. and M.F. acknowledge the Australian Research Council (ARC) for funding via the ARC Centre of Excellence for Electromaterials Science, grant CE140100012. The simulation work was supported by computational resources provided by the Australian Government through the National Computational Infrastructure national facility systems under the National Computational Merit Allocation Scheme. X.W. acknowledges the financial support of the Australia-India Strategic Research Fund (AISRF 48515).
The authors declare no competing interests.
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Chen, F., Wang, X., Armand, M. et al. Cationic polymer-in-salt electrolytes for fast metal ion conduction and solid-state battery applications. Nat. Mater. (2022). https://doi.org/10.1038/s41563-022-01319-w