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This study compares several electrolytes for application in electrochemical double layer capacitors (EDLCs), as well as their influence on double layer formation on different activated carbon materials. While propylene carbonate (PC) was used as electrolyte solvent in all cases, the applied conductive salt was varied. A change in conductive salt was found to have a great impact on solubility as well as the electrolytes' ion transport properties. Most importantly the choice of conductive salt strongly influenced the maximum operative potentials of PC based electrolytes, leading to EDLCs exhibiting maximum operative voltages as high as 3.5 V. Furthermore it was found that not only a high operative voltage, but also well adjusted transport properties are needed for an EDLC electrolyte in order to maximize the device's energy and power capabilities. Finally the electrolytes' influence on the capacitance of five activated carbon materials was studied, leading to the conclusion that in order to maximize energy storage in EDLCs, electrolyte and carbon material have to be adjusted one to another.

This study describes the use of mixtures of the ionic liquid (IL) trimethyl-sulfonium bis [(trifluoromethyl) sulfonyl]imide (Me 3 STFSI) and propylene carbonate (PC) as electrolytes for carbon-based electrochemical double layer capacitors (EDLCs). Two different mixtures have been investigated. The first one contained the maximum amount of Me 3 STFSI (3.8 mol L À1 ) soluble in PC at room temperature (RT). The second one contained 1.9 mol L À1 of Me 3 STFSI, which is the concentration featuring the highest conductivity among all possible mixtures between PC and Me 3 STFSI at RT. The physicochemical properties, including conductivity, viscosity, and electrochemical and thermal stability of both mixtures, have been initially investigated. Afterward, the use of these mixtures as electrolytes for EDLCs has been considered. This study showed that by using these innovative electrolytes, it is possible to develop EDLCs with an operative voltage as high as 3.0 V. It was clearly demonstrated that the EDLC cycle life strongly depends on the concentration of Me 3 STFSI present in the mixture. Moreover, it was also proved that mixtures containing high concentrations of IL are able to suppress anodic oxidation of the Al current collector at high potential. When a solution with a high salt concentration is used, an EDLC with high energy, high cycle life and a broad temperature range of operation can be realized.

The chemical binding of amorphous manganese oxide and carbon particles was achieved with the diazonium chemistry. The synthesis was performed in two steps, with a first step consisting in the surface functionnalization of carbon particles with aminophenyl groups and the subsequent attachment of amorphous manganese oxide particles through generated phenyl groups. The bond between carbon and MnO 2 particles is believed to occur between the carbon from the phenyl groups attached to carbon particles, and the oxygen atoms from the manganese oxide lattice. The capacitance of the carbon/MnO 2 grafted nanocomposite electrode is doubled compared to a simple mixture of its two components. The constant increment in the study and development of energy storage devices such as electrochemical capacitors (ECs) is related to an ever-growing demand of energy of the society. Electrochemical capacitors can be classified by their energy storage mechanisms in two main systems: 1) electrical double layer capacitance which arises from the charge separation at the electrode/electrolyte interface 1 and 2) pseudocapacitive charge storage phenomena where fast and reversible reactions take place.2 At this time, carbon is the commonly used electrode material for electrical double layer capacitor (EDLC) 3 while transition metal oxides and some conductive metal nitrides have demonstrated good performance as pseudocapacitive electrodes. 4 In terms of pseudocapacitive materials, manganese oxide (MnO 2 ) has proved to be one of the most promising materials due to its high energy density, low cost, environmental friendliness and natural abundance. 5 The initial studies describing the use of MnO 2 as an electrode material for ECs were performed by Lee and Goodenough. 6 They reported that amorphous or poorly crystallized MnO 2 powders incorporated into composite electrodes exhibited a capacitor-like electrochemical response in neutral KCl electrolyte, and delivered a specific capacitance of 200 F/g for "bulk" electrodes. Since this initial report, the interest in MnO 2 for ECs applications has grown steadily.Despite its electrochemical performance, the use of MnO 2 is still limited to moderate power applications due to its poor intrinsic electrical conductivity (10 −5 to 10 −6 S.cm −1 ). 7 Up to now, one of the most viable approaches to circumvent this major drawback is the use of a conductive additive such as carbon for improving the percolation through the electrode. For example, carbon black has been used just in a simple mixture with manganese oxide. 28 From all these studies it is clear that an intimate mixture of the carbon additive and manganese dioxide leads to improved power capability, but there is no clear trend to tell which carbon additive leads to the best electrode. However, carbon black is already widely used in ECs technology and thus it should be desirable to focus on this type of carbon when designing MnO 2 based electrode.In this study, we designed a new approach for the preparation of carbon/metal oxide composite electrod...