Mariachiara Lazzari

Role of Carbon Porosity and Ion Size in the Development of Ionic Liquid Based Supercapacitors

The role played by carbon porosity and electrolyte chemistry in the development of double-layer supercapacitors based on solvent-free ionic liquids ILs of a wide electrochemical stability window is investigated. Voltammetric studies performed in N-methyl-N-butyl-pyrrolidinium bis trifluoromethanesulfonyl imide PYR14TFSI , N-trimethyl-N-propylammonium bis trifluoromethanesulfonyl imide, and N-methyl-N-butyl-pyrrolidinium tris pentafluoroethyl trifluorophosphate ionic liquids and PYR14TFSI—tetraethyl ammonium bis trifluoromethanesulfonyl imide solutions demonstrate that the pore-to-ion size ratio and the porous electrode/IL interface properties may have a higher impact on the electrode electrical response than do the inherent IL bulk properties. The effect of carbon porosity on the electrode capacitance and charge storage capability in both the positive and negative potential domains is discussed in relation to the IL properties, and an estimation of the upper limits of the performance of IL based supercapacitors with carbons of optimized porosity is reported.

Dynamic Pulse Power and Energy of Ionic-Liquid-Based Supercapacitor for HEV Application

Asymmetric electrochemical double-layer carbon supercapacitors (AEDLCs) with N-methoxyethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 1(2O1) TFSI) ionic-liquid electrolyte can safely cycle above room temperature with maximum cell voltage as high as 3.7 V over several thousand cycles and are thus promising candidates for hybrid electric vehicle (HEV) applications. Here, we report the energy and power performance of the PYR 1(2O1) TFSI-based AEDLCs in the -30 to 60°C temperature range evaluated by the conventional galvanostatic cycling and by the United States Advanced Battery Consortium and the U.S. Department of Energy (DOE) FreedomCAR benchmark protocols. The most outstanding finding is that the ionic-liquid-based supercapacitor meets the dynamic power and energy capability targets stated by DOE for power-assist HEVs.

Lithiation/Delithiation Performance of Cu6Sn5 with Carbon Paper as Current Collector

Lithiation/delithiation of Cu 6 Sn 5 both electrochemically and mechanochemically prepared on a carbon paper (CP) current collector was investigated by repeated galvanostatic cycles with time-limited charges to insert different amounts of lithium per Sn atom (Li/Sn) into the alloy. The results demonstrated that, unlike Cu 6 Sn 5 electrodeposited on Cu foil, both electrochemical and mechanochemical Cu 6 Sn 5 on CP can undergo hundreds of lithiation/delithiation cycles with Li/Sn > 2 at high current density (0.74 mA cm - 2 ), thereby delivering constant amounts of charge with coulombic efficiency near 100%. The Cu 6 Sn 5 /CP electrodes with a loading of 6.6 mg cm - 2 and charge limited to 2.43 Li/Sn yielded a specific capacity of 330 mAh g - 1 and a capacity per geometric area of 2.18 mAh cm - 2 . These values compare well with those of graphite-based anodes of commercial batteries. The significant improvement in cyclability performance of the Cu 6 Sn 5 /CP electrodes is due to the CP current collectors three-dimensional conductive matrix, which preserves the electric contact over cycling so that alloy cracking becomes less detrimental for the electric contact.

Photochemical and photophysical properties of a poly(propylene amine) dendrimer functionalised with E-stilbene units

A second generation poly(propylene amine) dendrimer functionalized at the periphery with eight E-stilbene and eight 4-tert-butylbenzenesulfonyl units has been prepared. The absorption spectrum, fluorescence spectrum and decay, E<==>Z photoisomerization, and photocyclization of the Z-isomer of the stilbene units have been investigated in air equilibrated acetonitrile solutions. For comparison purposes, a reference compound of the peripheral dendrimer units, namely 4-tert-butyl-N-propyl-N-(4-styryl-benzyl)-benzenesulfonamide, has also been studied. The quantum yield of the E-->Z photoisomerization reaction (0.30) and the fluorescence quantum yield of the E isomer (0.014) are substantially smaller for the units appended to the dendrimer compared to those of the reference compound (0.50 and 0.046, respectively). The presence of a red tail and the biexponential decay of the emission band of the dendrimer indicate formation of excimers between the stilbene units appended at the poly(propylene amine) dendritic structure. Under the experimental conditions used (lambda(exc)= 313 nm), a Z/E photostationary state (around 9 : 1 for both reference compound and dendrimer ) is reached in the time scale of minutes. On continuing irradiation, other photoreactions take place in the time scale of hours: the stilbene moiety of compound undergoes photocyclization to phenanthrene (quantum yield 0.015), whereas in dendrimer photocyclization to phenanthrene is accompanied by other processes, including a photoreaction involving the internal amine groups.

ILHYPOS Ionic Liquid-Based Supercapacitors

This paper presents work carried out within a European Union project which led to the development of 3.7 V and 340 F pre-series electrochemical double-layer capacitor cell featuring an asymmetric configuration with positive and negative carbon electrodes of different weight and solvent-free ionic liquid electrolyte. Such supercapacitor design with nonvolatile and safe electrolyte provides a successful response to the requirement for power assist application in hybrid electric vehicles (HEVs).