Hybrid capacitors in organic, aqueous and ionic liquid electrolytes

François Béguin

 Poznan University of Technology 

Abstract: The two main electrochemical systems which may be applied to store energy are lithium-ion batteries (LIBs) and electrochemical capacitors (ECs). LIBs store the energy through redox reactions, and are characterized by a high energy density, moderate cycle life and power. ECs store energy through electrostatic forces using high surface area carbon electrodes, and thereof display high power and long cycle life, yet their energy density is relatively low [1]. Therefore, enhancing the specific energy of ECs in order to broaden the spectrum of their applications is an important driver for both researchers and industry players. In this context, internal hybridization of a battery-type electrode and a capacitor-type one is an elegant path to high energy devices, while keeping high power and long life span.

The best example is the lithium-ion capacitor (LIC) which implements an electrical double-layer (EDL) positive electrode made from porous carbon and a LIB faradaic negative electrode made from graphite or hard carbon, while using a lithium salt (LiPF6) in a mixture of organic solvents. For pre-intercalation of lithium in the graphite/carbon negative electrode, we recently introduced a new method where a sacrificial lithiated material (organic or oxide) is incorporated together with activated carbon in the positive electrode and oxidized irreversibly during an initial formation cycle [2,3]. The resulting LIC cells demonstrate excellent cycle life and ca. 4 times higher energy density than conventional EDLCs using the same carbon.

In an attempt to develop more environmentally friendly and cheaper ECs, we also developed AC/AC hybrid systems with redox active electrolytes. The AC/AC capacitors with mixed KI + Li2SO4 aqueous electrolyte can operate up to U = 1.6 V with twice higher capacitance than in Li2SO4, owing to trapping of polyiodides in the porosity of the positive electrode [4]. Similarly, a hybrid AC/AC device operating up to 2.0 V with a capacitance at the level of 200 F∙g-1 could be realized by implementing redox-active ionic liquids with pseudohalide anions [5]. The performance of the systems using various electrode and electrolyte materials will be critically compared during the presentation.

Biography: François Béguin was Professor and leader of the Energy & Environment Group in Orléans University (France) till 2011, and he is now Professor in Poznan University of Technology (Poland), where he leads the Power Sources Group (http://powersourcesgroup.put.poznan.pl).

His research activities are devoted to chemical and electrochemical applications of carbon materials, with a special attention to the development of nano-carbons with controlled porosity and surface functionality for applications to energy conversion/storage and environment protection. The main topics investigated in his research group are lithium- and sodium-ion batteries, electrochemical capacitors including hybrid capacitors, electrochemical hydrogen storage, reversible electrosorption of pollutants in water. He owns several patents related with the synthesis of nano-structured carbon materials (nanotubes, carbons from biomass, …) and their use for electrochemical systems. He published over 270 publications in high rank international journals and his works are cited in more than 15000 papers. His Hirsch index is H = 56.

He was also involved in several books dealing with carbon materials and energy storage. Recently, in the series “Materials for Sustainable Energy and Development”, Max Lu ed., he edited the book “Supercapacitors - Materials, Systems and Applications. He is a member of the International Advisory Board of the Carbon Conferences and he launched the international conferences on Carbon for Energy Storage and Environment Protection (CESEP). He is member of the editorial board of the journal Carbon, and Editor of Energy Storage Materials.

    In the French Agency for Research (ANR), he was Director of national programs on Energy Storage and Hydrogen and Fuel Cells till 2012.