Fabrizio Alessandrini

Synthesis of Hydrophobic Ionic Liquids for Electrochemical Applications

In this work is described an improved synthesis of hydrophobic room-temperature ionic liquids (RTIL) composed of N-methyl-N-alkylpyrrolidinium (or piperidinium) cations and (perfluoroalkylsulfonyl)imide, [(C n F 2n+1 SO 2 )(C m F 2m+1 SO 2 )N - ], anions. The procedure described allows the synthesis of hydrophobic ionic liquids with the purity required for electrochemical applications such as high-voltage supercapacitors and lithium batteries. This new synthesis does not require the use of environmentally unfriendly solvents such as acetone, acetonitrile, and alogen-containing solvents that are not suitable for industrial applications. Only water and ethyl acetate are used throughout the entire process. The effect of the reaction temperature, time, and stoichiometry in the various steps of the synthesis has been investigated. With an iterative purification step performed at the end of the synthesis, ultrapure, clear, colorless, inodorous RTILs were obtained. The final vacuum drying at 120°C gave RTILs with a moisture content below 10 ppm. Details for the synthesis of N-butyl-N-methylpyrrolidinium bis(trifluoromethansulfonyl)imide (PYR 14 TFSI) are reported. The overall yield for the synthesis of this ionic liquid was above 86 wt %. Electrochemical tests performed on this material are also reported.

Composite Polymer Electrolytes with Improved Lithium Metal Electrode Interfacial Properties I. Elechtrochemical Properties of Dry PEO‐LiX Systems

Several types of lithium ion conducting polymer electrolytes have been synthesized by hot-pressing homogeneous mixtures of the components, namely, poly(ethylene oxide) (PEO) as the polymer matrix, lithium trifluoromethane sulfonate (LiCF{sub 3}SO{sub 3}), and lithium tetrafluoroborate (LiBF{sub 4}), respectively, as the lithium salt, and lithium gamma-aluminate {gamma}-LiAlO{sub 2}, as a ceramic filler. This preparation procedure avoids any step including liquids so that plasticizer-free, composite polymer electrolytes can be obtained. These electrolyte have enhanced electrochemical properties, such as an ionic conductivity of the order of 10{sup {minus}4} S/cm at 80--90 C and an anodic breakdown voltage higher than 4 V vs. Li. In addition, and most importantly, the combination of the dry feature of the synthesis procedure with the dispersion of the ceramic powder, concurs to provide these composite electrolytes with an exceptionally high stability with the lithium metal electrode. In fact, this electrode cycles in these dry polymer electrolytes with a very high efficiency, i.e., approaching 99%. This in turn suggests the suitability of the electrolytes for the fabrication of improved rechargeable lithium polymer batteries.

Investigation on lithium–polymer electrolyte batteries

Abstract Lithium–polymer batteries using vanadium oxide-based composite electrodes and operating at moderate temperatures (∼90°C) have been investigated. The work was developed within the advanced lithium–polymer batteries for electric vehicles (ALPE) project, an Italian integrated project, devoted to the realization of lithium–polymer batteries for electric vehicle applications.

Comparison of Solvent-Cast and Hot-Pressed P ( EO ) 20LiN ( SO 2 CF 2 CF 3 ) 2 Polymer Electrolytes Containing Nanosized SiO2

Solvent-cast and hot-pressed P(EO) 2 0 LiN(SO 2 CF 2 CF 3 ) 2 (LiBETI) polymer electrolytes containing ceramic fillers such as 7 nm SiO 2 and 2-4 μm γ-LiAlO 2 were prepared. The ionic conductivity and interfacial stability of these poly(ethylene oxide) electrolytes were investigated. The addition of ceramic fillers to solvent-cast and hot-pressed P(EO) 2 0 LiBETI polymer electrolytes did not result in any substantial improvement of ionic conductivity. However, solvent-cast SiO 2 -containing P(EO) 2 0 LiBETI polymer electrolytes showed a much higher interfacial resistance and Li stripping overvoltage than hot-pressed and filler-free solvent-cast electrolytes.

Characterization of PEO‐Based Composite Cathodes. I. Morphological, Thermal, Mechanical, and Electrical Properties

This report describes the fabrication and characterization of polymer-based composite cathode membranes intended for use in polymer-electrolyte batteries operating at moderate temperatures (60--100 C). The present work is focused on the determination of morphological, thermal, mechanical, and electrical properties of PEO-based composite cathodes. The work was developed within the Advanced Lithium Polymer Electrolyte project (ALPE), an Italian integrated project devoted to the realization of lithium polymer batteries for electric vehicle applications.

Electrochemical testing of industrially produced PEO-based polymer electrolytes

Abstract The present report describes the results of the electrochemical tests performed on polyethyleneoxide-based polymer electrolyte thin films industrially manufactured by blown-extrusion. The polymer electrolyte composition was PEO 20 LiCF 3 SO 3 : 16.7% γLiAlO 2 . The polymer electrolyte film was tested to evaluate the ionic conductivity as well as the interfacial properties with lithium metal anodes. The work was developed within the advanced lithium polymer electrolyte (ALPE) project, an Italian project devoted to the realization of lithium polymer batteries for electric vehicle applications, in collaboration with Union Carbide.

Ionic Liquid Based Electrolytes for High Energy Electrochemical Storage Devices

Room temperature ionic liquids (RTILs) – salts which are liquids at or below room temperature – were first reported for ethylammonium nitrate [1] and have been extensively reported in recent years. RTILs are nonvolatile, nonflammable and often have excellent thermal stability. These materials have aroused the interests of researchers for a wide variety of applications including fuel cells, electrochemical capacitors, dye-sensitive solar cells, electrochemical device and batteries [2-7]. The use of RTILs as electrolytes in high energy electrochemical devices batteries is very promising because this may solve many of the problems of traditional liquid electrolytes that are volatility and flammability. The use of RTILs as replacements for conventional solvents in liquid electrolytes [6-8] and the incorporation of RTILs into solid polymer electrolytes [9,10] are under investigation worldwide. Among the large family of RTILs, salts with imidazolium based cations have received extensive attention due to their high conductivity. Unfortunately, imidazolium based RTILs have unfavorably chemical and electrochemical properties with lithium metal due to the presence of acidic cation protons. Recently, RTILs composed of N-alkyl-N-methylpyrrolidinium cations (PYR1R) (the subscript indicates the number of carbons in the alkyl group of the cation) and bis(trifluoromethanesulfonyl)imide anions (TFSI) (PYR1RTFSI) have been reported by MacFarlane et al. [11] and us [12-15]. Some of the pyrrolidinium salts such as PYR13TFSI and PYR14TFSI, have sub-ambient melting points and a high room temperature ionic conductivity. High energy density batteries are required as power source for applications such as telecommunications, portable electronic devices and hybrid electric vehicles (HEVs). Lithium-ion batteries are currently or soon will be the batteries of choice to obtain these objectives. The next generation lithium metal batteries (with lithium metal anodes rather than carbon intercalation anodes) require different, preferably solid-state, electrolytes. To achieve lighter, safer, longer life and higher energy density batteries, polymer electrolytes appear to be the most promising candidates, but their ionic conductivity at ambient-moderate temperatures is much too low (~10 S/cm). In recent work, we demonstrated that the incorporation of PYR13TFSI into P(EO)20LiTFSI polymer electrolytes results in free-standing membranes with a considerably increased room temperature ionic conductivity [12-14]. We also reported that Li/LiFePO4 batteries incorporating PYR13TFSI in the polymer electrolyte and the cathode can be reversibly operated even at moderate temperatures with a high discharge capacity. Supercapacitors, due to their capability to deliver high specific power during a few seconds or more, are presently considered as the electrical energy storage devices of choice for smoothing the strong and short-time power solicitations required in transportation and domestic applications powered by fuel cells or batteries, as well as for energy storage substations for voltage compensation in distributed networks. ILs display wide electrochemical stability windows and good conductivities so that they can be used as solvent-free “green” electrolytes for high voltage supercapacitors [1618]. The use of ILs has been investigated both in DLCSs [3,19-20] and in hybrid supercapacitors [21], but their cycling stability over a high number of cycles required by these power energy conversion systems still needed to be proven. In a recent work, the results of cycling tests over more than 15,000 cycles for an activated carbon (AC)//poly(3-methylthiophene) (pMeT) hybrid supercapacitor with PYR14TFSI, operating at 60°C and with an electrode mass loading suitable for practical applications [22]. In the present work we will report on the most recent results obtained at ENEA on IL for batteries and supercapacitors. A brief overview of the EU Project ILHYPOS (Ionic Liquid Hybrid Power Supercapacitors) will be also given.

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.

Overview of ENEA’s Projects on lithium batteries

Abstract The increasing need of high performance batteries in various small-scale and large-scale applications (portable electronics, notebooks, palmtops, cellular phones, electric vehicles, UPS, load levelling) in Italy is motivating the R&D efforts of various public and private organizations. Research of lithium batteries in Italy goes back to the beginning of the technological development of primary and secondary lithium systems with national know-how spread in various academic and public institutions with a few private stakeholders. In the field of lithium polymer batteries, ENEA has been dedicating significant efforts in almost two decades to promote and carry out basic R&D and pre-industrial development projects. In recent years, three major national projects have been performed and coordinated by ENEA in co-operation with some universities, governmental research organizations and industry. In these projects novel polymer electrolytes with ceramic additives, low cost manganese oxide-based composite cathodes, environmentally friendly process for polymer electrolyte, fabrication processes of components and cells have been investigated and developed in order to fulfill long-term needs of cost-effective and highly performant lithium polymer batteries.

Electrochemical characterization of a composite polymer electrolyte with improved lithium metal electrode interfacial properties

In the development of rechargeable lithium polymer batteries it is of paramount importance to control the passivation phenomena occurring at the lithium electrode interface. It is well estabilished that the type and the growth of the lithium passivation layer is unpredictably influenced by the presence of liquid components and/or impurities in the electrolyte. Therefore, one approach to improve the stability of the lithium interface is the use of liquid-free, highly pure electrolytes.The electrochemical properties of a composite polymer electrolyte obtained by hot pressing a mixture of polyethylene oxide (PEO), a lithium salt (lithium tetrafluoroborate, LiBF4) and a powdered ceramic additive (γ-LiAlO2), will be presented and discussed.The electrochemical characterization included the determination of the ionic conductivity, the anodic break-down voltage and, most importantly, the stability of the lithium metal electrode interface and the lithium stripping-plating process efficiency.The main feature of this dry, true solid-state electrolyte is a very good compatibility with the lithium metal electrode, demonstrated by a very high lithium cycling efficiency, which approaches a value of 99%.