Djamila Benrabah

Perfluorosulfonate-polyether based single ion conductors

New salts with monomer functionality and bearing a perfluorosulfonate group have been synthesized. These salts contain one or two carbon double bonds and thus can be incorporated into cross-linked solvating ionomers. Another family possesses epoxy rings and can be copolymerized with ethylene oxide. The results, in terms of ionic conductivities and thermal behavior are reported for these single-cation conductor polymer electrolytes. The conductivity values of these materials are markedly higher than those previously reported for other t + = 1 materials. The loss in conductivity, as compared to the untethered salt complexes, corresponds approximately to that attributed to the anionic conductivity. Alkali metals rank in the order σ K+ > σ Na+ > σ Li- .

COMPARATIVE ELECTROCHEMICAL STUDY OF NEW POLY(OXYETHYLENE)-LI SALT COMPLEXES

The high ionic conductivity of alkali-metal salts complexed with poly(oxyethylene)(POE) has stimulated wide research on solid polymer electrolytes. Differential scanning calorimetry (DSC), cyclic voltammetry and conductivity measurements have been used to explore the fundamental electrochemical characteristics of two new promising Li salts: Li[(CF3SO2)2N](LiTFSI) and Li[(CF3SO2)3C](LiTriTFSM). A study of the ionic conductivity of membranes containing various concentrations of lithium salts as a function of temperature reveals that, when compared with all the other salts used so far, these new compounds markedly improve the conductivities, essentially as a consequence of lower crystallinity. The voltammograms between –0.2 and 3.9 V vs. Li+/Li° show that the three anhydrous complexes POE–LiTFSI, POE–LiTriTFSM and POE–50%LiTFSI–50%LiTriTFSM have a wide electrochemical stability window.

Comparative ion transport in several polymer electrolytes

A comparative transport number study on a wide variety of lithium salts was performed, confirming the prevalence of an anionic transport in most of the usual salts dissolved in a polyether network. A cationic transport close to 0.5 was determined for several perfluorosulfonate-based polymer electrolytes. The method used confirmed a transport number close to unity for a perfluorosulfonate-based ionomer.

Comparative ab initio calculations on several salts

Ab initio calculations performed on three anions, substituted by strong electron withdrawing groups CF 3 SO 2 , brought useful information on the anion geometries and stabilities as well as on the charge delocalization. Thus the carbanion exhibits a planar optimized geometry while, according to HOMO values, the stability vs. oxidation is best for the imide anion. Moreover the absolute hardness, calculated from the HOMO and LUMO energy levels, show that this latter is the hardest base among the three previous anions.

Synthesis and electrochemical characterization of a new family of lithium salts

Abstract This paper deals with the chemical and electrochemical characterization of a novel lithium salt which has a bulky delocalized anion. This salt has been synthesized with a good overall yield by reacting (CF 3 SO 2 ) 2 CHNa with an acid chloride C 6 H 5 COCl. The crystallinity of high molecular weight host polymer POE is notably reduced by dissolution of the salt and, at room temperature, some complexes provide the best conductivities known up to now. Furthermore a microvoltammetry study has shown the wide electrochemical window of this salt.

Lithium organic salts with extra functionalities

Lithium perfluorosulfonate salts have been tailored either to provide solvating and/or plasticizing effect, or polar function. Adding these extra functionalities to the organic anion result in a good combination of ionic conductivity and cationic transference number. The high cationic conductivity obtained for polymer electrolytes at the concentration O/Li=30 must be emphasized.

New polyamide-ether electrolytes

Abstract A novel family of polyelectrolytes (polyamide-ether) has been synthesized in our laboratory by polycondensation between an α,ω-diamine poly(oxyethylene-co-oxypropylene) (Jeffamine® diamine) and terephthaloyl chloride in order to obtain linear systems. Crosslinked networks were prepared by reacting trimesic acid trichloride with diallylamine (DAA) (or N-methylallylamine (NMAA)) and Jeffamine®. Linear polyamides/LiTFSI with O/Li = 8 reached a conductivity of 10 −6 Ω −1 at room temperature, while the same value was obtained for the corresponding network at 30°C. X-Ray diffractograms show the amorphous character of these materials. Their conductivities are slightly lower than those of linear POE (mol.wt = 5 × 10 6 /LiTFSI (S. Sylla, J.Y. Sanchez and M. Armand, unpublished observations). This fact is most probably due to the great rigidity introduced by the network systems.

Cationic conductivity in poly(oxyethylene oxide) networks

Abstract New monomer salts with a perfluorosulfonate group were synthesized. These new salts, bearing one or two double bonds, lead to cross-linked solvating ionomers. Preliminary ionic conductivities and thermal characterizations are reported for single-cation conductors polymer electrolytes. The conductivity values of these single-cation conductors are markedly higher than those reported in the literature; the conductivity loss, with respect to the free-salt complexes, corresponds approximately to the expected anionic conductivity. The aim of this communication is twofold: (i) description of the synthesis of new lithium salts, and (ii) presentation of the results obtained with poly-electrolytes having a grafted anion.

Synthesis and electrochemical characterization of new bulky lithium salts

Abstract We describe the synthesis of new lithium salts, based on bulky carbanions, substituted by strong electron withdrawing groups together with their electrochemical studies using high molecular weight host polymer poly(oxyethylene) POE. The ionic conductivities of lithium salts-POE complexes have been measured as a function of temperature by impedance spectroscopy. The new lithium salts exhibit a wide electrochemical window stability. Their dissolution in POE ( M w =5×10 6 ) provides amorphous polymer electrolytes with high ionic conductivity.

Polymer and salt selection for lithium polymer batteries

Several network-based polymer electrolytes provide both thermal, mechanical and redox stabilities, while insuring a high conductivity level. Linear unsaturated polyether precursors may be obtained either by step-growth polymerization from oligomeric polyethers or by ring-opening polymerization from oxirane mixtures. In addition, theoretical investigations on several lithium salts are presented, which allowed optimized geometries as well as charge densities to be established in the gas phase.