Giovanni Battista Appetecchi

Nanocomposite polymer electrolytes for lithium batteries

Ionically conducting polymer membranes (polymer electrolytes) might enhance lithium-battery technology by replacing the liquid electrolyte currently in use and thereby enabling the fabrication of flexible, compact, laminated solid-state structures free from leaks and available in varied geometries. Polymer electrolytes explored for these purposes are commonly complexes of a lithium salt (LiX) with a high-molecular-weight polymer such as polyethylene oxide (PEO). But PEO tends to crystallize below 60 °C, whereas fast ion transport is a characteristic of the amorphous phase. So the conductivity of PEO–LiX electrolytes reaches practically useful values (of about 10−4 S cm−1) only at temperatures of 60–80 °C. The most common approach for lowering the operational temperature has been to add liquid plasticizers, but this promotes deterioration of the electrolytes mechanical properties and increases its reactivity towards the lithium metal anode. Here we show that nanometre-sized ceramic powders can perform as solid plasticizers for PEO, kinetically inhibiting crystallization on annealing from the amorphous state above 60 °C. We demonstrate conductivities of around 10−4 S cm−1 at 50 °C and 10−5 S cm−1 at 30 °C in a PEO–LiClO4 mixture containing powders of TiO2 and Al2O3 with particle sizes of 5.8–13 nm. Further optimization might lead to practical solid-state polymer electrolytes for lithium batteries.

Kinetics and stability of the lithium electrode in poly(methylmethacrylate)-based gel electrolytes

Abstract The transport and electrochemical properties of gel-type ionic conducting membranes formed by immobilizing liquid solutions of lithium salts in a poly(methylmethacrylate) matrix have been determined. In particular, the conductivity, the lithium ion transference number and the electrochemical stability window are evaluated and discussed. Finally, particular attention is devoted to the phenomena occuring at the interface between these ionic membranes and the lithium metal electrode.

Synthesis and characterization of highly conducting gel electrolytes

Abstract The electrochemical properties of gel electrolytes formed by the immobilization in a poly(acrylonitrile) matrix of solutions of common lithium salts ( eg LiClO 4 , LiAsF 6 and LiN(CF 3 SO 2 ) 2 ) in organic solvents ( eg the propylene carbonate—ethylene carbonate mixture, γ-butyrolactone or the γ-butyrolactone-ethylene carbonate mixture) have been determined. The results indicate that in accordance with previous literature data, these electrolytes have a high ionic conductivity, a wide electrochemical stability window and a high lithium transference number. However, their application in long-life, rechargeable lithium polymer batteries may be hindered by the instability of the negative electrode interface.

Transport and interfacial properties of composite polymer electrolytes

Lithium polymer electrolytes formed by dissolving a lithium salt LiX in poly(ethylene oxide) PEO, may find useful application as separators in lithium rechargeable polymer batteries. The main problems, which are still to be solved for a complete successful operation of these materials, are the reactivity of their interface with the lithium metal electrode and the decay of their conductivity at temperatures below 70°C. In this paper we demonstrate that a successful approach for overcoming these problems, is the dispersion of selected ceramic powders in the polymer mass, with the aim of developing new types of composite PEO–LiX polymer electrolytes characterized by enhanced interfacial stability, as well as by improved ambient temperature transport properties.

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.

Nanoscale organization in piperidinium-based room temperature ionic liquids

Here we report on the complex nature of the phase diagram of N-alkyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide ionic liquids using several complementary techniques and on their structural order in the molten state using small-wide angle x-ray scattering. The latter study indicates that the piperidinium aliphatic alkyl chains tend to aggregate, forming alkyl domains embedded into polar regions, similar to what we recently highlighted in the case of other ionic liquids.

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.

A New Class of Advanced Polymer Electrolytes and Their Relevance in Plastic‐like, Rechargeable Lithium Batteries

The synthesis, properties, and application of a new class of polymer electrolytes, are here reported and discussed. The electrolytes have a very high ionic conductivity, an acceptable lithium ion transport number, and a wide electrochemical stability window. The members of the family which appear most promising in terms of stability of the lithium electrode interface have been tested as electrolyte separators in high voltage, thin layer, laminated rechargeable batteries. Preliminary results provided indications of promising performance in terms of voltage output and cyclability.

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.

Investigation on the Stability of the Lithium‐Polymer Electrolyte Interface

In this paper is reported an investigation on the stability of the interface formed by polyethene oxide (PEO)-based polymer electrolytes in contact with lithium metal anodes. In particular, the investigation was oriented to determine the effect of the composite electrolyte preparation procedure and environment and the filler addition as well as the cell assembly procedure on the interfacial properties of PEO-LiCF 3 SO 3 /Li half cells. The stability investigation was performed at the operative temperature (90°C) of the electrolyte (PEO 20 LiCF 3 SO 3 ) in rest condition as well as during continuous lithium plating/stripping cycles. The results indicate that the preparation procedure and the environment play major roles with respect to the addition of the filler.