Bénédicte Claude-Montigny

Absorption ability and kinetics of a liquid electrolyte in PVDF–HFP copolymer containing or not SiO2

Abstract Gel polymer electrolytes have been prepared from PVDF–HFP copolymer with various silica contents incorporating Gamma valerolactone (VL) or VL/EC (80/20 in mole) (EC: ethylene carbonate) solutions of lithium bis(trifluoromethane sulfone) imide (LiTFSI). The influence of temperature, salt content and silica addition on the kinetics of absorption and wettability of the copolymer has been investigated. An empirical model, taking into account gel swelling during the absorption allows us to relate, at constant temperature, the wetting time and the volumetric fraction of trapped electrolyte, which is a critical factor for ionic conductivity of the gel. Increasing the silica content in the dry copolymer increases the porosity and consequently the rate of absorption and thus the amount of incorporated liquid phase at saturation. To a lower extent, an increase in the temperature of absorption has the same effects. The prepared gels have good mechanicals properties and conductivities. As an example, a gel of composition: PVDF – HFP / SiO 2 / VL / EC / LiTFSI of molar percentages 36/6.7/42/10.5/4.8 exhibits a conductivity of 2.9 mS cm − 1 at 293 K.

Conductive properties of polymer diacrylates incorporating solutions of lithium salts: Part I. Solvent–polymer and salt–solvent interactions

Abstract Gels were prepared by 1,3-butanediol diacrylate (BDD) or tetraethylene glycol diacrylate (TEG) polymerisation (UV irradiation with about 1 wt.% of benzoin methyl ether as initiator) in the presence of gamma butyrolactone (BL) or BL/LiN(CF 3 SO 2 ) 2 (LiTFSI) solutions which were incorporated in the polymer network. For the diacrylate/BL gels, the determination of molar polarisabilities and the Raman spectroscopic study allow to show that there is no specific interaction between the solvent and the polymer. The evolution of the ionic conductivity with the gel composition is related to the volumetric fraction of the liquid phase in the gel. The maximum absorption capacity of the diacrylate network towards the liquid phase is determined assuming a “cubic-like” structure. In order to compare, in the second part of this paper, the conductivities of the “free” and incorporated liquid phases, a simplified conductivity model is presented for the liquid electrolytes. In this article, the conductivity study is focused on the BDD/BL/LiTFSI electrolytes.

Conductivity study of diacrylate-based gels. Part III. Influence of the nature of the constituents and improvement of a theoretical model of ionic transport

Abstract Several gel electrolytes were prepared by incorporation of a liquid electrolyte in a polymer diacrylate network. The liquid electrolytes were solutions of lithium trifluoromethane sulfonate (LiTF) or lithium bis(trifluoromethane sulfone) imide (LiTFSI) in gamma butyrolactone (BL), gamma valerolactone (VL) and an optimized mixture of ethylene carbonate (EC) and 2-methoxyethyl ether (DG: diglyme) of molar percentage: EC/DG (45:55). The monomer diacrylates were: 1,3-butanediol diacrylate (BDD), 1,3-butanediol dimethacrylate (BDDM), ethylene glycol dimethacrylate (EGDM) and tetraethylene glycol diacrylate (TEG). The variation of conductivity with the polymer, solvent and lithium salt contents and with temperature was studied. The volumetric weight of these gels were also determined at room temperature. The experimental results were related to the competitive salt solvent and salt polymer interactions, quantified through a theoretical model of ionic conductivity. The ionic transport in the gel electrolytes was assumed to be of the liquid type. The decrease in ionic conductivity of the liquid electrolyte, enclosed in the polymer network, relative to the “free” liquid solution, is due to the fixation of some fraction of the salt on the polymer, to increase of the viscosity of the media and to a tortuous path for the ion migration. From the proposed model, the conductivity variations with the gel composition as well as with the nature of the constituents are explained.

Conductive properties of polymer diacrylates incorporating solutions of lithium salts: Part II. Model of ionic transport in the gel in relation with the polymer network structure

Abstract Gamma butyrolactone (BL) or BL/LiN(CF 3 SO 2 ) 2 (LiTFSI) solutions were incorporated in the polymer network of 1,3-butanediol diacrylate (BDD) or tetraethylene glycol diacrylate (TEG) polymerized under UV irradiation with about 1 wt.% of benzoin methyl ether as initiator. The evolution of the ionic conductivity, determined by ac impedance technique, with both gel composition and temperature, is related to the ions–solvent and ions–polymer interactions, assuming a cubic lattice structure for the polymer network. The decrease in conductivity from the “free” liquid phase to the incorporated liquid phase is due to both a dynamic equilibrium of solvation of ions between the solvent and the polymer, and, for the “free” ions, a drastic decrease in their mobility because of long-range interactions with the polymer. These interactions are quantified in terms of a “fixation equilibrium constant” and a “microscopic viscosity” relative to ion mobility in the gel. In addition, the moving of ions is not straight in the gel and a tortuosity coefficient in relation with the gel composition is defined.