D. Deroo

Poly(dimethylsiloxane)-poly(ethylene oxide) based polyurethane networks used as electrolytes in lithium electrochemical solid state batteries

Abstract Ionic conductivity and redox stability domain of a new type of polymer electrolyte have been studied. The polymer electrolytes were prepared from a network of poly (dimethylsiloxane-grafted ethylene oxide) copolymer crosslinked by an aliphatic isocyanate (grafted PDMS) and containing 10 wt% LiClO 4 . Ionic conductivities higher than 10 −5 ω −1 cm −1 are obtained above 30°C. The study of the electrochemical stability of the crosslinking agent suggests that the unreacted isocyanate groups are not stable. The electroactivity domain of the grafted PDMS-LiClO 4 10 wt% electrolyte is larger than 3 V. The performances of a solid state battery using this electrolyte have been investigated. The first discharge and charge depths were 73%. The rechargeability behaviour have been compared with those of a Li/RuO 2 battery with a linear high molecular weight P(EO) 8 -LiClO 4 as electrolyte.

Modelling the voltammetric study of intercalation in a host structure: application to lithium intercalation in RuO2

Abstract Intercalation process kinetics have been studied theoretically for the case of potential sweep voltammetry. The influence of the thickness (or the particle radius) of the “host” material and the potential sweep rate has been determined between the limits of thin film diffusion and semi-infinite diffusion for a reversible process. Experimental data have been obtained with the cell: RuO2/LiClO4-PEO/Li. The theoretical results have been used to calculate the diffusion coefficient of lithium in the “host” structure RuO2 at 80°C, giving an approximate value of 1.6 × 10−11 cm2 s−1

Potentiometric measurements of ionic transport parameters in poly(ethylene oxide)-LiX electrolytes

An electrochemical technique based on concentration cell e.m.f. measurements is used to determine the lithium transference number and diffusion coefficient in poly(ethylene oxide)-lithium salt complexes. Measurements were carried out at 90°C on PEO−LiI, PEO−LiClO4 and PEO−LiCF3SO3 electrolytes. According to the phase diagram of the PEO-lithium salt system these complexes are fully amorphous at 90°C. Accurate determination oftLi+ by the e.m.f. concentration cell method generally requires knowledge of the mean salt activity coefficients. However, this becomes unnecessary when the two electrolyte concentrations differ only slightly. As a first step the mean salt activity coefficient was estimated using a galvanic cell of the lithium/PEO-LiX/MXn/M type withMn+=Ag+ or Pb2+, and X−=I− or CF3SO3−. The resulting lithium transference numbers are 0.34 for the PEO−LiI complex and 0.7 for PEO−LiCF3SO3. Discrepancies between thetLi+ values can be explained by the formation of triplets in the PEO−LiCF3SO3 electrolyte. By recording concentration cell potential versus time and comparing with theoretical curves, the salt lithium diffusion coefficient was obtained.DLiI was found to be around 4×10−8 cm2 s−1 in PEO−LiI and 8×10−8 cm2 s−1 in PEO−LiCF3SO3 at 90°C. These results suggest a liquid-like behaviour for the microscopic transport mechanism.

Potentiometric measurements of ionic mobilities in poly(ethyleneoxide) electrolytes

Abstract An electrochemical technique based on concentration cell E.M.F. measurements was used to determine the lithium transference number and the salt coefficient diffusion in PEO-lithium salts complexes. Measurements were carried out at 90°C on PEOLiI, PEOLiClO 4 and PEOLiCF 3 SO 3 t Li + is found to be 0.7 for PEOLiCF 3 SO 3 and 0.3 for both PEOLiI and PEOLiClO 4 D LiX is approximatively 3 to 4 10 −8 cm 2 s −1 for both PEOLiI and PEOLiClO 4 and 7 to 8 10 −8 cm 2 s −1 for PEOLiCF 3 SO 3 .

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.

A galvanostatic study of lithium intercalation in RuO2

Abstract The diffusion process in a host structure has been studied at constant current with the cells: RuO 2 composite/ LiClO 4 PEO/Li and RuO 2 powder/LiClO 4 PC/Li. The effect of grain size distribution and temperature has been investigated and the diffusion coefficient for Li in RuO 2 calculated along with the diffusion activation energy (0.52 eV). Results show no intercalation of PC at 25°C.

Thermodynamical insertion of lithium in V5S8. Validity domain of the Thompson method

Abstract EMF versus Li-composition relation is determined by electrochemical insertion for Li-V 5 S 8 . The values of the thermodynamic functions Δ G , Δ H , Δ S corresponding to the lithium insertion reaction have been deduced. The Thompson method (electrochemical potential spectroscopy) has been applied to the V 5 S 8 cathode, but it appears not valid in our case. The calculation of current versus time function is made to analyze the validity of this method. This technique requires: fast diffusion of Li in the host material, small grain size, small increments of applied voltage, low value of the cut-off current.