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Biredox ionic liquids with solid-like redox density in the liquid state for high-energy supercapacitors



Kinetics of electrochemical reactions are several orders of magnitude slower in solids than in liquids as a result of the much lower ion diffusivity. Yet, the solid state maximizes the density of redox species, which is at least two orders of magnitude lower in liquids because of solubility limitations. With regard to electrochemical energy storage devices, this leads to high-energy batteries with limited power and high-power supercapacitors with a well-known energy deficiency. For such devices the ideal system should endow the liquid state with a density of redox species close to the solid state. Here we report an approach based on biredox ionic liquids to achieve bulk-like redox density at liquid-like fast kinetics. The cation and anion of these biredox ionic liquids bear moieties that undergo very fast reversible redox reactions. As a first demonstration of their potential for high-capacity/high-rate charge storage, we used them in redox supercapacitors. These ionic liquids are able to decouple charge storage from an ion-accessible electrode surface, by storing significant charge in the pores of the electrodes, to minimize self-discharge and leakage current as a result of retaining the redox species in the pores, and to raise working voltage due to their wide electrochemical window.

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Figure 1: Comparison of charge storage in EDLC with IL electrolyte and the biredox IL-enhanced pseudocapacitor.
Figure 2: Synthesis of the biredox ionic liquid.
Figure 3: Electrochemistry of the biredox IL in the supercapacitors.
Figure 4: Self-discharge of supercapacitors.
Figure 5: Ragone plot of supercapacitors using various electrolytes.
Figure 6: Specific capacitance retention on cycling in biredox IL electrolyte.


  1. 1

    Rolison, D. R. & Nazar, L. F. Electrochemical energy storage to power the 21st century. MRS Bull. 36, 486–493 (2011).

    CAS  Article  Google Scholar 

  2. 2

    Augustyn, V. et al. High-rate electrochemical energy storage through Li+ intercalation pseudocapacitance. Nat. Mater. 12, 518–522 (2013).

    CAS  Article  Google Scholar 

  3. 3

    Wagemaker, M., van Eck, E. R. H., Kentgens, A. P. M. & Mulder, F. M. Li-ion diffusion in the equilibrium nanomorphology of spinel Li4+xTi5O12 . J. Phys. Chem. B 113, 224–230 (2009).

    CAS  Article  Google Scholar 

  4. 4

    Merlet, C. et al. On the molecular origin of supercapacitance in nanoporous carbon electrodes. Nat. Mater. 11, 306–310 (2012).

    CAS  Article  Google Scholar 

  5. 5

    Merlet, C. et al. Highly confined ions store charge more efficiently in supercapacitors. Nat. Commun. 4, 2701 (2013).

    CAS  Article  Google Scholar 

  6. 6

    Duduta, M. et al. Semi-solid lithium rechargeable flow battery. Adv. Energy Mater. 1, 511–516 (2011).

    CAS  Article  Google Scholar 

  7. 7

    Dunn, B., Kamath, H. & Tarascon, J.-M. Electrical energy storage for the grid: a battery of choices. Science 334, 928–935 (2011).

    CAS  Article  Google Scholar 

  8. 8

    Bruce, P. G., Scrosati, B. & Tarascon, J.-M. Nanomaterials for rechargeable lithium batteries. Angew. Chem. Int. Ed. 47, 2930–2946 (2008).

    CAS  Article  Google Scholar 

  9. 9

    Choi, N.-S. et al. Challenges facing lithium batteries and electrical double-layer capacitors. Angew. Chem. Int. Ed. 51, 9994–10024 (2012).

    CAS  Google Scholar 

  10. 10

    Weissmann, M., Crosnier, O., Brousse, T. & BÃclanger, D. Electrochemical study of anthraquinone groups, grafted by the diazonium chemistry, in different aqueous media-relevance for the development of aqueous hybrid electrochemical capacitor. Electrochim. Acta 82, 250–256 (2012).

    CAS  Article  Google Scholar 

  11. 11

    Yang, Z. et al. Electrochemical energy storage for green grid. Chem. Rev. 111, 3577–3613 (2011).

    CAS  Article  Google Scholar 

  12. 12

    Chmiola, J. et al. Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer. Science 313, 1760–1763 (2006).

    CAS  Article  Google Scholar 

  13. 13

    Simon, P. & Gogotsi, Y. Materials for electrochemical capacitors. Nat. Mater. 7, 845–854 (2008).

    CAS  Article  Google Scholar 

  14. 14

    Merlet, C., Rotenberg, B., Madden, P. A. & Salanne, M. Computer simulations of ionic liquids at electrochemical interfaces. Phys. Chem. Chem. Phys. 15, 15781–15792 (2013).

    CAS  Article  Google Scholar 

  15. 15

    Huang, J., Sumpter, B. G. & Meunier, V. Theoretical model for nanoporous carbon supercapacitors. Angew. Chem. Int. Ed. 47, 520–524 (2008).

    CAS  Article  Google Scholar 

  16. 16

    Feng, G. et al. The importance of ion size and electrode curvature on electrical double layers in ionic liquids. Phys. Chem. Chem. Phys. 13, 1152–1161 (2011).

    CAS  Article  Google Scholar 

  17. 17

    Kondrat, S. & Kornyshev, A. Superionic state in double-layer capacitors with nanoporous electrodes. J. Phys. Condens. Matter 23, 022201 (2011).

    CAS  Article  Google Scholar 

  18. 18

    Armand, M., Endres, F., MacFarlane, D. R., Ohno, H. & Scrosati, B. Ionic-liquid materials for the electrochemical challenges of the future. Nat. Mater. 8, 621–629 (2009).

    CAS  Article  Google Scholar 

  19. 19

    Frackowiak, E., Lota, G. & Pernak, J. Room-temperature phosphonium ionic liquids for supercapacitor application. Appl. Phys. Lett. 86, 164104 (2005).

    Article  Google Scholar 

  20. 20

    Varzi, A., Balducci, A. & Passerini, S. Natural cellulose: a green alternative binder for high voltage electrochemical double layer capacitors containing ionic liquid-based electrolytes. J. Electrochem. Soc. 161, A368–A375 (2014).

    CAS  Article  Google Scholar 

  21. 21

    Brandt, A. & Balducci, A. Theoretical and practical energy limitations of organic and ionic liquid-based electrolytes for high voltage electrochemical double layer capacitors. J. Power Sources 250, 343–351 (2014).

    CAS  Article  Google Scholar 

  22. 22

    Shim, Y. & Kim, H. J. Nanoporous carbon supercapacitors in an ionic liquid: a computer simulation study. ACS Nano 4, 2345–2355 (2010).

    CAS  Article  Google Scholar 

  23. 23

    Brousse, T., Bélanger, D. & Long, J. W. To be or not to be pseudocapacitive? J. Electrochem. Soc. 162, A5185–A5189 (2015).

    CAS  Article  Google Scholar 

  24. 24

    Simon, P., Gogotsi, Y. & Dunn, B. Where do batteries end and supercapacitors begin? Science 343, 1210–1211 (2014).

    CAS  Article  Google Scholar 

  25. 25

    Conway, B. E. Transition from “supercapacitor’ to “battery” behavior in electrochemical energy storage. J. Electrochem. Soc. 138, 1539–1548 (1991).

    CAS  Article  Google Scholar 

  26. 26

    Lota, G. & Frackowiak, E. Striking capacitance of carbon/iodide interface. Electrochem. Commun. 11, 87–90 (2009).

    CAS  Article  Google Scholar 

  27. 27

    Lota, G., Fic, K. & Frackowiak, E. Alkali metal iodide/carbon interface as a source of pseudocapacitance. Electrochem. Commun. 13, 38–41 (2011).

    CAS  Article  Google Scholar 

  28. 28

    Senthilkumar, S. T., Selvan, R. K., Lee, Y. S. & Melo, J. S. Electric double layer capacitor and its improved specific capacitance using redox additive electrolyte. J. Mat. Chem. A 1, 1086–1095 (2013).

    CAS  Article  Google Scholar 

  29. 29

    Senthilkumar, S. T., Selvan, R. K. & Melo, J. S. Redox additive/active electrolytes: a novel approach to enhance the performance of supercapacitors. J. Mat. Chem. A 1, 12386–12394 (2013).

    CAS  Article  Google Scholar 

  30. 30

    Yu, H. et al. A novel redox-mediated gel polymer electrolyte for high-performance supercapacitor. J. Power Sources 198, 402–407 (2012).

    CAS  Article  Google Scholar 

  31. 31

    Wang, Y., Cardona, C. M. & Kaifer, A. E. Molecular orientation effects on the rates of heterogeneous electron transfer of unsymmetric dendrimers. J. Am. Chem. Soc. 121, 9756–9757 (1999).

    CAS  Article  Google Scholar 

  32. 32

    Sathyamoorthi, S., Suryanarayanan, V. & Velayutham, D. Organo-redox shuttle promoted protic ionic liquid electrolyte for supercapacitor. J. Power Sources 274, 1135–1139 (2015).

    CAS  Article  Google Scholar 

  33. 33

    Ghilane, J., Fontaine, O., Martin, P., Lacroix, J. C. & Randriamahazaka, H. Formation of negative oxidation states of platinum and gold in redox ionic liquid: electrochemical evidence. Electrochem. Commun. 10, 1205–1209 (2008).

    CAS  Article  Google Scholar 

  34. 34

    Fontaine, O. et al. Mass transport and heterogeneous electron transfer of a ferrocene derivative in a room-temperature ionic liquid. J. Electroanalyt. Chem. 632, 88–96 (2009).

    CAS  Article  Google Scholar 

  35. 35

    Chen, X. et al. Imidazolium functionalized TEMPO/iodide hybrid redox couple for highly efficient dye-sensitized solar cells. J. Mat. Chem. A 1, 8759–8765 (2013).

    CAS  Article  Google Scholar 

  36. 36

    Yu, H. et al. Redox-active alkaline electrolyte for carbon-based supercapacitor with pseudocapacitive performance and excellent cyclability. RSC Adv. 2, 6736–6740 (2012).

    CAS  Article  Google Scholar 

  37. 37

    Xie, H. J., Gélinas, B. & Rochefort, D. Redox-active electrolyte supercapacitors using electroactive ionic liquids. Electrochem. Commun. 66, 42–45 (2016).

    CAS  Article  Google Scholar 

  38. 38

    Rosanske, T. W. & Evans, D. H. Rate constants for the electrode reactions of some quinones in aprotic media at platinum, gold and mercury electrodes. J. Electroanal. Chem. Interfacial Electrochem. 72, 277–285 (1976).

    CAS  Article  Google Scholar 

  39. 39

    Gupta, N. & Linschitz, H. Hydrogen-bonding and protonation effects in electrochemistry of quinones in aprotic solvents. J. Am. Chem. Soc. 119, 6384–6391 (1997).

    CAS  Article  Google Scholar 

  40. 40

    Chuang, C.-M., Huang, C.-W., Teng, H. & Ting, J.-M. Hydrothermally synthesized RuO2/Carbon nanofibers composites for use in high-rate supercapacitor electrodes. Compos. Sci. Technol. 72, 1524–1529 (2012).

    CAS  Article  Google Scholar 

  41. 41

    Conway, B. E., Birss, V. & Wojtowicz, J. The role and utilization of pseudocapacitance for energy storage by supercapacitors. J. Power Sources 66, 1–14 (1997).

    CAS  Article  Google Scholar 

  42. 42

    He, S. & Chen, W. High performance supercapacitors based on three-dimensional ultralight flexible manganese oxide nanosheets/carbon foam composites. J. Power Sources 262, 391–400 (2014).

    CAS  Article  Google Scholar 

  43. 43

    Hubig, S. M., Rathore, R. & Kochi, J. K. Steric control of electron transfer. Changeover from outer-sphere to inner-sphere mechanisms in arene/quinone redox pairs. J. Am. Chem. Soc. 121, 617–626 (1999).

    CAS  Article  Google Scholar 

  44. 44

    Bard, A. J. Inner-sphere heterogeneous electrode reactions. Electrocatalysis and photocatalysis: the challenge. J. Am. Chem. Soc. 132, 7559–7567 (2010).

    CAS  Article  Google Scholar 

  45. 45

    Chen, L., Bai, H., Huang, Z. & Li, L. Mechanism investigation and suppression of self-discharge in active electrolyte enhanced supercapacitors. Energy Environ. Sci. 7, 1750–1759 (2014).

    CAS  Article  Google Scholar 

  46. 46

    Randriamahazaka, H. & Asaka, K. Electromechanical analysis by means of complex capacitance of bucky-gel actuators based on single-walled carbon nanotubes and an ionic liquid. J. Phys. Chem. C 114, 17982–17988 (2010).

    CAS  Article  Google Scholar 

  47. 47

    Roldán, S., Blanco, C., Granda, M., Menéndez, R. & Santamaría, R. Towards a further generation of high-energy carbon-based capacitors by using redox-active electrolytes. Angew. Chem. Int. Ed. 50, 1699–1701 (2011).

    Article  Google Scholar 

  48. 48

    Forster, R. J. & O’Kelly, J. P. Protonation reactions of anthraquinone-2,7-disulphonic acid in solution and within monolayers. J. Electroanal. Chem. 498, 127–135 (2001).

    CAS  Article  Google Scholar 

  49. 49

    Zhang, J. & Zhao, X. S. Conducting polymers directly coated on reduced graphene oxide sheets as high-performance supercapacitor electrodes. J. Phys. Chem. C 116, 5420–5426 (2012).

    CAS  Article  Google Scholar 

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S.A.F. is indebted to la Chaire Total de la foundation Balard for the position of an invited professor at the Institute Charles Gerhardt, Montpellier, France, as well as the Austrian Federal Ministry of Economy, Family and Youth and the Austrian National Foundation for Research, Technology and Development and funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 636069).

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E.M. and L.C. contributed equally to this work and carried out the experiments. O.F., F.F. and S.A.F. conceived and designed the experiments, directed the project and analysed the results. F.F., S.A.F. and O.F. co-wrote the manuscript. A.V. and A.M. helped with synthesis of anionic species. All authors contributed to the discussion and interpretation of the results.

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Correspondence to Olivier Fontaine.

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Mourad, E., Coustan, L., Lannelongue, P. et al. Biredox ionic liquids with solid-like redox density in the liquid state for high-energy supercapacitors. Nature Mater 16, 446–453 (2017).

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