Engineering high-energy-density sodium battery anodes for improved cycling with superconcentrated ionic-liquid electrolytes

Abstract

Non-uniform metal deposition and dendrite formation in high-density energy storage devices reduces the efficiency, safety and life of batteries with metal anodes. Superconcentrated ionic-liquid electrolytes (for example 1:1 ionic liquid:alkali ion) coupled with anode preconditioning at more negative potentials can completely mitigate these issues, and therefore revolutionize high-density energy storage devices. However, the mechanisms by which very high salt concentration and preconditioning potential enable uniform metal deposition and prevent dendrite formation at the metal anode during cycling are poorly understood, and therefore not optimized. Here, we use atomic force microscopy and molecular dynamics simulations to unravel the influence of these factors on the interface chemistry in a sodium electrolyte, demonstrating how a molten-salt-like structure at the electrode surface results in dendrite-free metal cycling at higher rates. Such a structure will support the formation of a more favourable solid electrolyte interphase, accepted as being a critical factor in stable battery cycling. This new understanding will enable engineering of efficient anode electrodes by tuning the interfacial nanostructure via salt concentration and high-voltage preconditioning.

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Fig. 1: Interfacial layering structure of ILs through AFM force measurement and MD simulations.
Fig. 2: Analysis of the numbers of different ions in the innermost interfacial layer.
Fig. 3: Na–FSI coordination in the innermost electrolyte layer.
Fig. 4: Electrochemical experiments at 50 °C on a Na|50 mol% NaFSI in C3mpyrFSI|Na symmetric cell with different preconditioning treatments.

Data availability

The data represented in Figs. 1–4 are provided with the paper as source data. All other data that support the findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

D.A.R., F.C., M.F., P.C.H. and A.N.S. acknowledge the Australian Research Council (ARC) for funding via the Australian Centre for Electromaterials Science, grant CE140100012. M.F. acknowledges ARC grant DP160101178. The simulation work was undertaken with the assistance of resources provided at the NCI National Facility systems at the Australian National University through the National Computational Merit Allocation Scheme supported by the Australian Government. D.A.R. thanks S. Begić and E. Jónsson for mentoring in simulation skills.

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M.F. conceived the idea. M.F. and F.C. directed the project. D.A.R. conducted MD simulations supervised by F.C. and M.F. and conducted the AFM experiment with the guidance of R.A. and H.L. The electrochemical experiment was conducted by S.A.F. with the participation of T.P. and supervised and interpreted by P.C.H. Interpretation of the results and preparation of the manuscript were carried out by D.A.R., F.C. and M.F. with discussion, comments and editing from R.A., P.C.H. and A.N.S.

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Correspondence to Fangfang Chen or Maria Forsyth.

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Rakov, D.A., Chen, F., Ferdousi, S.A. et al. Engineering high-energy-density sodium battery anodes for improved cycling with superconcentrated ionic-liquid electrolytes. Nat. Mater. (2020). https://doi.org/10.1038/s41563-020-0673-0

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