Book of Abstracts

International Symposium on Enhanced Electrochemical Capacitors
7th Annual edition

11st-15th July 2022 Bologna, Italy

 

Hybrid Supercapacitors based on Manganese oxide and Activated carbon Electrodes Using Sodium Exchange Aquivion Electrolyte Membrane

Francesco Lufrano, Minju Thomas, Svetlana Veleva, Boriana Karmanova, Antonino Brigandì, Ana Arenillas, Antonia Stoyanova

The current scenario of energy storage and generation is demanding higher energy density supercapacitors. We need economic and green systems to adapt to the recent climate policies as well. Supercapacitors are eco-friendly energy storage devices with high power density and long-life cycle. There are mainly three different configuration of supercapacitor, symmetric, asymmetric, and hybrid based on the electrode material. Symmetric cells are constructed using identical materials in both electrodes. The performance of symmetric capacitor is limited by their small voltage window and lower energy density. Hybrid supercapacitors with asymmetric configuration are new alternatives with relatively high energy density compared to their symmetric counter parts. Generally, different materials are used in each electrode to design both the asymmetric cells or hybrid cells.

Manganese oxide (MnO₂) is a well-known electrode material for supercapacitor, due to its high theoretical capacitance (1370 F/g), stability in aqueous electrolyte, low toxicity and very low cost. Charging and discharging occurs mainly by fast surface redox reactions occurring in manganese oxide materials electrode with the help of cations (e.g. K⁺, H⁺, Na⁺). Apart from its good electrochemical behavior, MnO2 suffers from a low electronic conductivity and in a limited potential range. The performance of MnO2 electrodes might be enhanced by combining the oxide with electrically conductive carbon materials. Herein, we report the synthesis of MnO₂ by a simple co-precipitation technique and its use as the positive electrode of the supercapacitor. Hybrid supercapacitors with asymmetric configuration has been constructed with a commercial activated carbon as negative electrode, MnO₂ as positive electrode and Na⁺ exchange Aquivion membrane that has the dual function of separator and electrolyte. The hybrid cell exhibited well rectangular voltammograms at different scan rates and exhibiting high specific capacitance of 124 F/g at 0.2 A/g and energy density of 11 Wh kg^-1. In addition, the type of hybrid supercapacitor was able to withstand harsh cycling by combining galvanostatic charging and discharging and floating conditions (i.e. 140 hours at 1.6 V) for up to 10,000 cycles without affecting the capacitance stability. Self-discharge studies on the cell were carried out, after 10000 charge discharge cycles. The cell was charged at 1.6 V for 3 h, then during the self-discharge, it retained more than 1 V up to 400 min. Further, the well EDLC behavior of the cell was improved by using a combination of MnO₂ - carbon as positive electrode and activated carbon as negative electrode. Well rectangular cyclic voltammograms was exhibited for the fast charge discharge rates. The modified cell showed a high specific capacitance of about 100 F/g at 0.2 A/g. The synergistic effect of MnO₂ and carbon resulted in a perfectly reversible charge storage redox processes, which occurs at the positive electrode. A detailed electrochemical study of these cells was carried out and compared with the symmetric carbon/carbon supercapacitor. A comprehensive analysis will be given during presentation.

 

Optimizing the pair carbon xerogels-electrolyte for high performance supercapacitors

L. Soserov, B. Karamanova, S. Veleva, A. Arenillas, F. Lufrano and A. Stoyanova

Supercapacitors have received a lot of research attention and are promising energy storage devices due to their high power and long cycle life. In order to developed an advanced device with significant capacity for storing charge and cheap carbon materials, efforts must focus not only on improving synthesis by controlling the morphology and pore size, but also on improving electrode-electrolyte compatibility of the resulting systems.

The present study examines the relationship between the surface chemistry of different kind activated carbon xerogels, the electrolyte type and the electrochemical properties of supercapacitors. 

Activated carbon xerogels were prepared by varying the initial pH of the resorcinol-formaldehyde aqueous solution (AX6.5, AX5.97, pH=6.5 and 5.97, respectively). One hybrid carbon xerogel-graphene (AX GO) have been investigated. This material has both a high porosity and an superior electrical conductivity.  The materials produced are physicochemical characterized by DTA/TGA, porous characterization and SEM analysis.

The carbon xerogel based electrodes were prepared by spreading over glass plate a slurry containing the carbon gel, graphite and poly vinylidene difluoride (PVDF) binder. The layer formed was dried consecutively at different temperatures, and then detached by water. After, the layer was dried again to improve its mechanical stability.

The developed electrode materials and the Aquivion® E87-05S membrane (Solvay Specialty Polymers), socked in Na₂SO₄ as a polymer electrolyte were used to assembly the solid-state supercapacitor. Symmetric supercapacitor cells composed by same electrodes and 1 M KOH electrolytes are also assembled and tested for comparison.

The supercapacitor performances are verified by different electrochemical methods - cyclic voltammetry, galvanostatic charge/discharge measurements and long-term durability tests in neutral and alkaline electrolytes.

Specific capacitances, energy and power density, energy efficiencies and durability were compared into studied supercapacitors. The results are discussed on the basis of electrode-electrolyte interaction and obtained correlations could be of importance in order to design sustainable solid-state supercapacitors with high power and energy density.

 

Effect of polymer-based electrolyte on electrochemical properties of supercapacitor systems

S. Veleva, B.Karamanova, A. Stoyanova, A. Arenillas, N. Rey

For the purposes of the present study, a polymeric ionic liquid based on pyrrolidine was produced. The anion exchange method was applied to a quaternized poly (diallyl methyl ammonium iodide) previously synthesized by the team. The obtained PIL was characterized by modern physicochemical methods and was used as an electrolyte in supercapacitor systems.

Two-electrode electrochemical cells based on activated carbon YP-50F a commercial product of the company "Kuraray Europe" or synthesized carbon xerogel, Ni-Mn phosphates as poly-composite electrodes and an electrolyte containing PIL, IL and LiBF₄ were assembled. CV-curves, galvanostatic charging / discharging and long term tests were performed, with the help of which the capacitive characteristics and the stability of the developed supercapacitors were monitored. The correlation between polymer electrolyte composition and structure and morphology of studied electrode materials was discussed.