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


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.


  1. 1.

    Fedorov, M. V. & Kornyshev, A. A. Ionic liquids at electrified interfaces. Chem. Rev. 114, 2978–3036 (2014).

    CAS  Article  Google Scholar 

  2. 2.

    Xu, K. Electrolytes and interphases in Li-ion batteries and beyond. Chem. Rev. 114, 11503–11618 (2014).

    CAS  Article  Google Scholar 

  3. 3.

    Cheng, X. B. et al. A review of solid electrolyte interphases on lithium metal anode. Adv. Sci. 3, 1–20 (2015).

    Google Scholar 

  4. 4.

    Lin, D., Liu, Y. & Cui, Y. Reviving the lithium metal anode for high-energy batteries. Nat. Nanotechnol. 12, 194–206 (2017).

    CAS  Article  Google Scholar 

  5. 5.

    Cheng, X. B., Zhang, R., Zhao, C. Z. & Zhang, Q. Toward safe lithium metal anode in rechargeable batteries: a review. Chem. Rev. 117, 10403–10473 (2017).

    CAS  Article  Google Scholar 

  6. 6.

    Lee, B., Paek, E., Mitlin, D. & Lee, S. W. Sodium metal anodes: emerging solutions to dendrite growth. Chem. Rev. 119, 5416–5460 (2019).

    CAS  Article  Google Scholar 

  7. 7.

    Watanabe, M. et al. Application of ionic liquids to energy storage and conversion materials and devices. Chem. Rev. 117, 7190–7239 (2017).

    CAS  Article  Google Scholar 

  8. 8.

    Mezger, M. et al. Molecular layering of fluorinated ionic liquids at a charged sapphire (0001) surface. Surf. Sci. 322, 424–428 (2008).

    CAS  Google Scholar 

  9. 9.

    Mao, X. et al. Self-assembled nanostructures in ionic liquids facilitate charge storage at electrified interfaces. Nat. Mater. 18, 1350–1357 (2019).

    CAS  Article  Google Scholar 

  10. 10.

    Black, J. M. et al. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy. Sci. Rep. 6, 1–12 (2016).

    Article  CAS  Google Scholar 

  11. 11.

    Black, J. M. et al. Bias-dependent molecular-level structure of electrical double layer in ionic liquid on graphite. Nano Lett. 13, 5954–5960 (2013).

    CAS  Article  Google Scholar 

  12. 12.

    Smith, A. M., Lee, A. A. & Perkin, S. The electrostatic screening length in concentrated electrolytes increases with concentration. J. Phys. Chem. Lett. 7, 2157–2163 (2016).

    CAS  Article  Google Scholar 

  13. 13.

    Su, Y.-Z., Fu, Y.-C., Yan, J.-W., Chen, Z.-B. & Mao, B.-W. Double layer of Au(100)/ionic liquid interface and its stability in imidazolium-based ionic liquids. Angew. Chem. Int. Ed. 48, 5148–5151 (2009).

    CAS  Article  Google Scholar 

  14. 14.

    Elbourne, A. et al. Nanostructure of the ionic liquid-graphite Stern layer. ACS Nano 9, 7608–7620 (2015).

    CAS  Article  Google Scholar 

  15. 15.

    Motobayashi, K., Minami, K., Nishi, N., Sakka, T. & Osawa, M. Hysteresis of potential-dependent changes in ion density and structure of an ionic liquid on a gold electrode: in situ observation by surface-enhanced infrared absorption spectroscopy. J. Phys. Chem. Lett. 4, 3110–3114 (2013).

    CAS  Article  Google Scholar 

  16. 16.

    Nanbu, N., Sasaki, Y. & Kitamura, F. In situ FT-IR spectroscopic observation of a room-temperature molten salt|gold electrode interphase. Electrochem. Commun. 5, 383–387 (2003).

    CAS  Article  Google Scholar 

  17. 17.

    Rubim, J. C., Trindade, F. A., Gelesky, M. A., Aroca, R. F. & Dupont, J. Surface-enhanced vibrational spectroscopy of tetrafluoroborate 1-n-butyl-3-methylimidazolium (BMIBF4) ionic liquid on silver surfaces. J. Phys. Chem. C. 112, 19670–19675 (2008).

    CAS  Article  Google Scholar 

  18. 18.

    Yuan, Y.-X., Niu, T.-C., Xu, M.-M., Yao, J.-L. & Gu, R.-A. Probing the adsorption of methylimidazole at ionic liquids/Cu electrode interface by surface-enhanced Raman scattering spectroscopy. J. Raman Spectrosc. 41, 516–523 (2010).

    CAS  Article  Google Scholar 

  19. 19.

    Baldelli, S. Surface structure at the ionic liquid-electrified metal interface. Acc. Chem. Res. 41, 421–431 (2008).

    CAS  Article  Google Scholar 

  20. 20.

    Hu, Z., Vatamanu, J., Borodin, O. & Bedrov, D. A molecular dynamics simulation study of the electric double layer and capacitance of [BMIM][PF6] and [BMIM][BF4] room temperature ionic liquids near charged surfaces. Phys. Chem. Chem. Phys. 15, 14234–14247 (2013).

    CAS  Article  Google Scholar 

  21. 21.

    Begić, S., Li, H., Atkin, R., Hollenkamp, A. F. & Howlett, P. C. A comparative AFM study of the interfacial nanostructure in imidazolium or pyrrolidinium ionic liquid electrolytes for zinc electrochemical systems. Phys. Chem. Chem. Phys. 18, 29337–29347 (2016).

    Article  CAS  Google Scholar 

  22. 22.

    Forsyth, M. et al. Tuning sodium interfacial chemistry with mixed-anion ionic liquid electrolytes. ACS Appl. Mater. Interfaces 11, 43093–43106 (2019).

    CAS  Article  Google Scholar 

  23. 23.

    Liu, Z. et al. Dendrite-free nanocrystalline zinc electrodeposition from an ionic liquid containing nickel triflate for rechargeable Zn-based batteries. Angew. Chem. Int. Ed. 55, 2889–2893 (2016).

    CAS  Article  Google Scholar 

  24. 24.

    Li, H., Endres, F. & Atkin, R. Effect of alkyl chain length and anion species on the interfacial nanostructure of ionic liquids at the Au(111)-ionic liquid interface as a function of potential. Phys. Chem. Chem. Phys. 15, 14624–14633 (2013).

    CAS  Article  Google Scholar 

  25. 25.

    Atkin, R. et al. AFM and STM studies on the surface interaction of [BMP]TFSA and [EMIm]TFSA ionic liquids with Au(111). J. Phys. Chem. C 113, 13266–13272 (2009).

    CAS  Article  Google Scholar 

  26. 26.

    Carstens, T., Lahiri, A., Borisenko, N. & Endres, F. [Py1,4]-FSI-NaFSI-based ionic liquid electrolyte for sodium batteries: Na+ solvation and interfacial nanostructure on Au(111). J. Phys. Chem. C 120, 14736–14741 (2016).

    CAS  Article  Google Scholar 

  27. 27.

    Hoffmann, V. et al. Influence of a silver salt on the nanostructure of a Au(111)/ionic liquid interface: an atomic force microscopy study and theoretical concepts. Phys. Chem. Chem. Phys. 20, 4760–4771 (2018).

    CAS  Article  Google Scholar 

  28. 28.

    Lahiri, A., Carstens, T., Atkin, R., Borisenko, N. & Endres, F. In situ atomic force microscopic studies of the interfacial multilayer nanostructure of LiTFSI-[Py1, 4]TFSI on Au(111): influence of Li+ ion concentration on the Au(111)/IL interface. J. Phys. Chem. C 119, 16734–16742 (2015).

    CAS  Article  Google Scholar 

  29. 29.

    Girard, G. M. A. et al. Spectroscopic characterization of the SEI layer formed on lithium metal electrodes in phosphonium bis(fluorosulfonyl)imide ionic liquid electrolytes. ACS Appl. Mater. Interfaces 10, 6719–6729 (2018).

    CAS  Article  Google Scholar 

  30. 30.

    Yoon, H., Howlett, P. C., Best, A. S., Forsyth, M. & MacFarlane, D. R. Fast charge/discharge of Li metal batteries using an ionic liquid electrolyte. J. Electrochem. Soc. 160, 1629–1637 (2013).

    Article  CAS  Google Scholar 

  31. 31.

    Forsyth, M. et al. Novel Na+ ion diffusion mechanism in mixed organic-inorganic ionic liquid electrolyte leading to high Na+ transference number and stable, high rate electrochemical cycling of sodium cells. J. Phys. Chem. C 120, 4276–4286 (2016).

    CAS  Article  Google Scholar 

  32. 32.

    Zhang, H. et al. Ionic liquid electrolyte with highly concentrated LiTFSI for lithium metal batteries. Electrochimica Acta 285, 78–85 (2018).

    CAS  Article  Google Scholar 

  33. 33.

    Choudhury, S. et al. Designing solid-liquid interphases for sodium batteries. Nat. Commun. 8, 1–10 (2017).

    Article  CAS  Google Scholar 

  34. 34.

    Periyapperuma, K. et al. Towards high rate Li metal anodes: enhanced performance at high current density in a superconcentrated ionic liquid. J. Mater. Chem. A 8, 3574–3579 (2020).

  35. 35.

    Wakeham, D., Nelson, A., Warr, G. G. & Atkin, R. Probing the protic ionic liquid surface using X-ray reflectivity. Phys. Chem. Chem. Phys. 13, 20828–20835 (2011).

    CAS  Article  Google Scholar 

  36. 36.

    Chen, F., Howlett, P. & Forsyth, M. Na-ion solvation and high transference number in superconcentrated ionic liquid electrolytes: a theoretical approach. J. Phys. Chem. C 122, 105–114 (2018).

    CAS  Article  Google Scholar 

  37. 37.

    Haskins, J. B., Bauschlicher, C. W. & Lawson, J. W. Ab Initio simulations and electronic structure of lithium-doped ionic liquids: structure, transport, and electrochemical stability. J. Phys. Chem. B 119, 14705–14719 (2015).

    CAS  Article  Google Scholar 

  38. 38.

    Matsumoto, K., Okamoto, Y., Nohira, T. & Hagiwara, R. Thermal and transport properties of Na[N(SO2F)2]-[N-methyl-N-propylpyrrolidinium][N(SO2F)2] ionic liquids for Na secondary batteries. J. Phys. Chem. C 119, 7648–7655 (2015).

  39. 39.

    Vicent-Luna, J. M. et al. Quantum and classical molecular dynamics of ionic liquid electrolytes for Na/Li-based batteries: molecular origins of the conductivity behavior. ChemPhysChem 17, 2473–2481 (2016).

    CAS  Article  Google Scholar 

  40. 40.

    Giffin, G. A., Moretti, A., Jeong, S. & Passerini, S. Decoupling effective Li+ ion conductivity from electrolyte viscosity for improved room-temperature cell performance. J. Power Sources 342, 335–341 (2017).

    CAS  Article  Google Scholar 

  41. 41.

    Gao, X., Wu, F., Mariani, A. & Passerini, S. Concentrated ionic-liquid-based electrolytes for high-voltage lithium batteries with improved performance at room temperature. ChemSusChem 12, 4185–4193 (2019).

    CAS  Article  Google Scholar 

  42. 42.

    Wróbel, P., Kubisiak, P. & Eilmes, A. Interactions in sodium bis(fluorosulfonyl)imide/1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide electrolytes for Na-ion batteries: insights from molecular dynamics simulations. J. Phys. Chem. C 123, 14885–14894 (2019).

    Article  CAS  Google Scholar 

  43. 43.

    Tsuzuki, S., Hayamizu, K. & Seki, S. Origin of the low-viscosity of [emim][(FSO2)2N] ionic liquid and its lithium salt mixture: experimental and theoretical study of self-diffusion coefficients, conductivities, and intermolecular interactions. J. Phys. Chem. B 114, 16329–16336 (2010).

    CAS  Article  Google Scholar 

  44. 44.

    Takenaka, N. et al. Microscopic formation mechanism of solid electrolyte interphase film in lithium-ion batteries with highly concentrated electrolyte. J. Phys. Chem. C 122, 2564–2571 (2018).

    CAS  Article  Google Scholar 

  45. 45.

    Makhlooghiazad, F. et al. Phosphonium plastic crystal salt alloyed with a sodium salt as a solid-state electrolyte for sodium devices: phase behaviour and electrochemical performance. J. Mater. Chem. A 5, 5770–5780 (2017).

    CAS  Article  Google Scholar 

  46. 46.

    Yang, H. et al. N-ethyl-N-propylpyrrolidinium bis(fluorosulfonyl)amide ionic liquid electrolytes for sodium secondary batteries: effects of Na ion concentration. J. Phys. Chem. C 123, 22018–22026 (2019).

    CAS  Article  Google Scholar 

  47. 47.

    Periyapperuma, K. et al. High Zn concentration pyrrolidinium-dicyanamide-based ionic liquid electrolytes for Zn2+/Zn0 electrochemistry in a flow environment. ACS Appl. Energy Mater. 1, 4580–4590 (2018).

    CAS  Article  Google Scholar 

  48. 48.

    Lindahl, E., Hess, B. & van der Spoel, D. GROMACS 3.0: a package for molecular simulation and trajectory analysis. Mol. Model. Annu. 7, 306–317 (2001).

    CAS  Article  Google Scholar 

  49. 49.

    Wang, R., Bi, S., Presser, V. & Feng, G. Systematic comparison of force fields for molecular dynamic simulation of Au(111)/ionic liquid interfaces. Fluid Phase Equilib. 463, 106–113 (2018).

    CAS  Article  Google Scholar 

  50. 50.

    Vatamanu, J., Xing, L., Li, W. & Bedrov, D. Influence of temperature on the capacitance of ionic liquid electrolytes on charged surfaces. Phys. Chem. Chem. Phys. 16, 5174–5182 (2014).

    CAS  Article  Google Scholar 

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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).

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