Patrice Simon1 2 Léo Nègre1 2 Barbara Daffos1 2 Pierre-Louis Taberna1

1, Univ Paul Sabatier-Toulouse III, Toulouse, , France
2, RS2E, FR CNRS 3459, Amiens, , France

Electrochemical Capacitors (ECs), also known as supercapacitors [1], have now reached the technical maturity for complementing- and sometimes replacing- batteries in a broad range of applications. Conventional electrolytes based on acetonitrile or propylene carbonate solvents have been mainly used in combination with ammonium cations and fluoride anions. Designing solid electrolytes for ECs would be of great interest to solve packaging issues, corrosion, self-discharge or leaks. Moreover these solid electrolytes could be used for flexible supercapacitors applications.
Ionogels are quasi-solid electrolyte obtained from the trapping of an Ionic Liquid (IL) into a silica scaffold using a sol-gel process [2]. In a first part, we will present the electrochemical performance of ionogel electrolytes and carbon-based supercapacitor cells using ionogel electrolytes [3,4]. Cyclic voltammetries and electrochemical impedance spectroscopy plots in a large temperature range (-40°C to +60°C) of cells will be presented and discussed. We will show that porous carbon materials can achieve high capacitance (90 F.g-1) in these solid-state like electrolytes thanks to the ionic liquid confinement in carbon nanopores (pore size < 1 nm). In a second step, we will present the results of an in-situ X-Ray scattering study combined with modelling to explain the confinement effect of ionic liquids trapped into carbon nanopores [5]. In such confined environment, ionic liquids ions can form co-ion pairs by breaking the Coulombic ordering rules, leading to an increase of capacitance thanks to the existence of a superionic state theoretically proposed by Kornyshev et al [6].

[1] Simon and Y. Gogotsi, Nature Materials, 7 (2008) 845-854.
[2] M. Brachet, T. Brousse, J. Le Bideau, ECS Elec. Letters, 11 (2014) A112-A115.
[3] L. Negre, B. Daffos, P.L. Taberna and P. Simon, JECS 162 (2015) A5037-A5040.
[4] L. Nègre, B. Daffos, P.L. Taberna and P. Simon, Electrochimica Acta 206, 490-495 (2016).
[5] R. Futamura, T. Iiyama, Y. Takasaki, Y. Gogotsi, M. J. Biggs, M. Salanne, J. Ségalini, P. Simon, K. Kaneko, Nature Materials (2017), DOI: 10.1038/nmat4974
[6] S. Kondrat and A. Kornyshev, J. Phys.: Condens. Matter 23, 022201- 022205 (2011).