Maria Montanino

Physical and Electrochemical Properties of N-Alkyl-N-methylpyrrolidinium Bis(fluorosulfonyl)imide Ionic Liquids: PY13FSI and PY14FSI

Two ionic liquids based upon N-alkyl-N-methylpyrrolidinium cations (PY(1R)(+)) (R=3 for propyl or 4 for butyl) and the bis(fluorosulfonyl)imide (FSI(-)), N(SO2F)2(-), anion have been extensively characterized. The ionic conductivity and viscosity of these materials are found to be among the highest and lowest, respectively, reported for aprotic ionic liquids. Both ionic liquids crystallize readily on cooling and undergo several solid-solid phase transitions on heating prior to melting. PY13FSI and PY14FSI are found to melt at -9 and -18 degrees C, respectively. The thermal stability of PY13FSI and PY14FSI is notably lower than for the analogous salts with the bis(trifluoromethanesulfonyl)imide (TFSI(-)), N(SO2CF3)2(-), anion. Both ionic liquids have a relatively wide electrochemical stability window of approximately 5 V.

Electrochemical and Physicochemical Properties of PY14FSI -Based Electrolytes with LiFSI

We report here the characterization of Li battery electrolytes based upon the N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid (PY 14 FSI) with lithium bis(fluorosulfonyl)imide (LiFSI) as a support salt. These electrolytes show low viscosity relative to other pyrrolidinium-based ionic liquids (ILs) and corresponding higher conductivity at subambient temperatures. The melting point of the IL decreases with the addition of LiFSI and concentrated samples remain totally amorphous. The electrolytes exhibit decreased thermal stability and increased parasitic cathodic reactions with increasing LiFSI fraction relative to the pure IL, probably due to a higher impurity level for the commercial LiFSI. Despite this, the electrolytes have excellent lithium cycling behavior at 20°C.

Melting Behavior and Ionic Conductivity in Hydrophobic Ionic Liquids

Four room-temperature ionic liquids (RTILs) based on the N-butyl-N-methyl pyrrolidinium (Pyr(14)(+)) and N-methyl-N-propyl pyrrolidinium cations (Pyr(13)(+)) and bis(trifluoromethanesulfonyl)imide (TFSI(-)) and bis(fluorosulfonyl)imide (FSI(-)) anions were intensively investigated during their melting. The diffusion coefficients of (1)H and (19)F were determined using pulsed field gradient (PFG) NMR to study the dynamics of the cations, anions, and ion pairs. The AC conductivities were measured to detect only the motion of the charged particles. The melting points of these ionic liquids were measured by DSC and verified by the temperature-dependent full width at half-maximum (FWHM) of the (1)H and (19)F NMR peaks. The diffusion and conductivity data at low temperatures gave information about the dynamics at the melting point and allowed specifying the way of melting. In addition, the diffusion coefficients of (1)H (D(H)) and (19)F (D(F)) and conductivity were correlated using the Nernst-Einstein equation with respect to the existence of ion pairs. Our results show that in dependence on the cation different melting behaviors were identified. In the Pyr(14)-based ILs, ion pairs exist, which collapse above the melting point of the sample. This is in contrast to the Pyr(13)-based ILs where the present ion pairs in the crystal dissociate during the melting. Furthermore, the anions do not influence the melting behavior of the investigated Pyr(14) systems but affect the Pyr(13) ILs. This becomes apparent in species with a higher mobility during the breakup of the crystalline IL.

Ionic Liquid Binary Mixtures for Low Temperature Applications

The thermal and transport properties of PYR1(2O1)TFSI-PYR13FSI ionic liquid binary mixtures as electrolytes for low temperature electrochemical devices are reported in the present paper. The DSC measurements are in good agreement with the conductivity results. It is shown that the incorporation of even small mole fractions (x  0.3) of PYR1(2O1)TFSI into PYR13FSI strongly hinders the ability of the samples to crystallize. This results in a very large conductivity enhancement for the PYR1(2O1)TFSI-PYR13FSI binary mixtures, particularly at low temperatures, that were seen to approach conduction values of 10-4 Scm-1 and 10-3 Scm-1 at -40°C and -20°C, respectively. Such an interesting behavior makes PYR1(2O1)TFSI-PYR13FSI binary mixtures particularly appealing for low temperature applications.

Electrolytes for rechargeable lithium batteries

Abstract Rechargeable lithium-ion batteries (RLIB) are excellent candidates for the next-generation power sources because of their high gravimetric and volumetric energy with respect to other cell chemistries. Actually, RLIBs supply most of the portable electronic devices (e.g., mobile phones, digital cameras, and laptops) and power tools. Recently, lithium battery applications have been expanding for several technologies, such as aerospace technology, electric vehicles, hybrid electric vehicles, and storage from renewable power sources. The lithium-ion battery technology is based on the use of electrode materials able to reversibly intercalate lithium cations, which are transferred between two host structures (positive and negative electrodes) during the charge and discharge processes. Commercial lithium-ion batteries commonly use liquid electrolytes based on suitable lithium salts (generally LiPF6) and organic solvents (generally alkylcarbonates such as EC, DEC, DMC), volatile and flammable, which represent a major problem for device safety. This issue has strongly pushed the scientific community toward the investigation of alternative, highly safe solvents. In recent years, gel polymer electrolytes have progressively replaced the above-mentioned liquid electrolytes. Additionally, a wide variety of alternative solvents as well as additives have been proposed, mainly aiming to improve the safety (flame retardants) and the compatibility (redox shuttles) of the electrolytes with high-voltage cathodes. In addition, completely dry, solvent-free electrolytes, both polymeric and inorganic, are under investigation worldwide because of the possibility to realize all solid-state lithium batteries, which are undoubtedly appealing from safety and engineering points of view and open new perspectives on applications. Finally, a new class of nonvolatile and nonflammable fluids, called ionic liquids (e.g., molten salts at room temperature), were successfully proposed in place of hazardous and toxic organic solvents for lithium battery electrolytes. Here, a survey of the most appealing types of electrolytes, proposed for modern rechargeable lithium batteries and taking a look at future trends is reported.

Highly conductive PEDOT:PSS on flexible substrate as ITO-free anode for polymer solar cells

In this work, highly conductive anode based on PEDOT:PSS is proposed as substitute of Indio-Tin Oxide (ITO) in flexible solar cells. The anodic conductive polymer was spin coated on a 125 μm thick polyethylene naphthalate (PEN) substrate. The obtained film was characterized in terms of structure and physical- chemical proprieties. The obtained results are very promising and the conductive film will be investigated in future as electrode in a complete polymeric solar cell.

Improving the gravure printed PEDOT:PSS electrode by gravure printing DMSO post-treatment

The poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most attractive conducting polymers proposed as electrode for flexible electronics. Promising methods for enhancing its low conductivity, main limit for its use, are based on post-treatment. However, most of them are not suitable for mass production. In this study, the gravure printing technique was tried for the post-treatment of the PEDOT layer using dimethylsulfoxide (DMSO), as practical, safe and cost effective process for improving the printed electrode. An increase of the conductivity of the printed PEDOT:PSS layer was found and attributed to the rearrangement of the polymeric chains that leads to the formation of PEDOT-rich regions improving the conducting pathways. In addition, smoother film surface and improved stability to the humidity were obtained, representing further advantages for its employment in plastic electronics. Therefore, the feasibility and the efficacy of the DMSO post-treatment of the PEDOT:PSS films by gravure printing were demonstrated, showing the way for the low cost all in-line industrial production of large area PEDOT:PSS electrodes.