Properties Of Gel Polymer Electrolytes Research Articles

Spectromechanical Properties of Polymeric Gel Electrolytes and Blends

AbstractIn this paper we studied the spectro‐mechanical properties of polymer gel electrolytes and blends by means of shear rheology. These electrolytes were obtained by immobilizing EC/PC/LiClO4 solutions in a polymeric matrix of PEO, PAN and PMMA, respectively. Two structural and thermoreversible transitions, a strong‐to‐weak gel and a gel‐to‐sol, were revealed and discussed. Moreover, PMMA‐PVdF blends have been studied as a function of the different polymeric ratios in order to obtain the best compromise between ionic conduction and mechanical properties. Interesting mechanical properties were observed at some intermediate blend compositions.

The electrochemical redox processes in PMMA gel electrolytes—behaviour of transition metal complexes

Electrochemical properties of polymer gel electrolytes based on polymethylmethacrylate (PMMA) were studied by cyclic voltammetry and impedance spectroscopy using new solid-state PMMA–Cd–Cd 2+ reference electrode. The suitable potential window of the PC–PMMA system was estimated from –0.2 to + 1.5 V versus Cd–Cd 2+. New polymer gels containing ferrocene–ferricinium (Fc–Fc +) couple and other transition metal complexes were prepared by the direct polymerisation of methylmethacrylate (MMA) monomer and the solution of metal complex and supporting electrolyte in anhydrous aprotic solvent—propylene carbonate (PC). The half-wave potentials and apparent diffusion coefficients of used complexes and their dependence on the composition of the system (liquid or gel) were estimated. Time dependent electrochemical measurements showed almost three order decrease of the diffusion coefficients of ferrocene (Fc) and ferricinium (Fc +) cation from 6 × 10 −5 to 2 × 10 −9 cm 2 s −1 during the polymerisation from the liquid to the polymer state. The results show that the PC–PMMA gel electrolyte can be described as a system of embedded solvent in the polymer network of PMMA without present monomer.

PMMA-based aprotic gel electrolytes

Aprotic electrolytes are essential for lithium batteries, electrochromic windows, electrochemical supercapacitors and similar systems. These materials can be also used in the solid-state electrochemical sensors. This paper deals with the basic properties of gel polymer electrolytes based on propylene carbonate immobilised by polymethylmethacrylate (MMA) as a part of their systematic research. Electric conductivity, metal electrodeposition from gels containing cadmium perchlorate and properties of ferrocene/ferricinium redox couple were investigated.

Structure and transport properties of polymer gel electrolytes based on PVdF-HFP and LiN(C 2F 5SO 2) 2

Gel polymer electrolytes composed of PVdF/HFP and a non-aqueous lithium electrolyte solution EC/DEC/LiN(C 2F 5SO 2) 2 (BETI) were prepared to investigate the conduction properties of the gel materials. Structural and micro-structural characterization was carried out by means of modulated differential scanning calorimetry (MDSC) and scanning electron microscopy (SEM). The samples with polymer/solution weight ratios higher than 0.5 contain at least an amorphous swollen gel phase and a crystalline one, while a pure liquid phase appears, which occupies cavities in the micrometer range in the gels with lower polymer content. The transport properties of the gels were investigated by means of impedance spectroscopy for conductivity and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) for diffusion coefficients. The results were compared with those of corresponding films prepared with LiN(CF 3SO 2) 2 (TFSI). The BETI-based samples showed diffusion values lower than the TFSI-based ones. Estimation of the carrier concentration change with the gel composition revealed that the interaction between the host polymer and the electrolyte in the gel especially in the polymer rich region (>50 wt%).

Ionic Conduction Properties of PVDF−HFP Type Gel Polymer Electrolytes with Lithium Imide Salts

Conduction properties of gel polymer electrolytes composed of lithium imide salts, LiN(CF3SO2)2, LiN(C2F5SO2)2, and PVDF−HFP copolymer were investigated using the pulsed-field gradient NMR and complex impedance techniques. The diffusion coefficients of the gel decreased with an increase in the polymer fraction in the gel. Carrier concentration exhibited 3 orders of magnitude variation in the fraction change in polymer from 80% to 20%. These results suggest that the polymer interacts with the electrolyte to affect the carrier concentration and mobility of the gel electrolytes. The interactive effect of polymer would be detected in the measurements of spin−lattice relaxation time (T1). The deviation of the symmetric curve of the temperature dependence of T1 could be divided into two components, one was consistent with the component of solution and independent of the polymer fraction and the other depended on the polymer fraction in the gel.

Electrochemical properties of polymer gel electrolytes based on poly(vinylidene fluoride) copolymer and homopolymer

Polymer gel electrolytes were prepared by soaking poly(vinylidene fluoride) (PVdF) membranes, obtained by casting solutions of PVdF copolymer or homopolymers in a solvent such as acetone, tetrahydrofuran (THF), methyl ethyl ketone (MEK) and N-methylpyrollidone (NMP), into an electrolyte solution of 1 M LiBF 4 in propylene carbonate (PC). During the casting process, phase separation occurred leading to non- or low-porous membranes when the phase separation remained in its early stage or to highly porous membranes when it was mostly achieved. The phase separation was enhanced with the increase in the polymer crystallinity and was more significant in the case of the homopolymers. The membranes cast from NMP solutions were non- or low-porous and showed very low uptakes of the electrolyte solution and low conductivity. In this case, the copolymer showed higher uptakes of the electrolyte solution than the homopolymers. It was also found that even for an equivalent uptake of the electrolyte solution the conductivity was higher for the copolymer than the homopolymer, attributable to the lowest crystallinity of the copolymer. On the contrary, the membranes obtained from MEK solutions with slow evaporation rates were highly porous for the homopolymers and absorb much more electrolyte solution than non- or low-porous membranes. The polymer electrolytes from the porous membranes exhibited conductivity of 10 −3 S/cm at 30°C. The phase separation process was very important since it allowed a higher uptake of the electrolyte solution and thus a higher conductivity. Nevertheless, increasing porosity affected the mechanical properties of the membranes when it exceeded 50% of the total volume. The principal limitation of the uptake of electrolyte was caused by the loss of mechanical strength. Concerning the potential window and the evolution of the interfacial resistance at the Li/polymer electrolyte interface, no significant difference could be pointed out between the copolymer and the homopolymers.