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

Abstract

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 Na2:1 NaFSI/PolyILNa 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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Fig. 1: Cation–anion coordination in PolyILs.
Fig. 2: Diffusion of ions and analysis of the correlation between fast or slow ions.
Fig. 3: Analysis of metal ion cage restructure and ion transport for the K12 and Na12 systems.
Fig. 4: The thermal properties, ionic conductivities and electrochemical properties of PDADMA-based PEs.

Data availability

The data that support the findings of this study are available from the corresponding authors upon reasonable request. Source data are provided with this paper.

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Acknowledgements

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).

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F.C., X.W. and M.F. conceived the idea. F.C. directed the project and conducted the computational work. X.W. conducted the experiments. The results were discussed with M.F and M.A. All authors participated in manuscript preparation.

Corresponding authors

Correspondence to Fangfang Chen, Xiaoen Wang or Maria Forsyth.

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Nature Materials thanks Renaud Bouchet and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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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

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