Z. A. Ibrahim

Conductivity enhancement due to ion dissociation in plasticized chitosan based polymer electrolytes

Abstract Cast films of chitosan acetate, plasticized chitosan acetate, chitosan acetate containing salt and plasticized chitosan acetate–salt complexes were used to obtain some insight on the mechanism of ionic conductivity in chitosan-based polymer electrolytes. The films are largely amorphous. The conductivity is due to the mobile ions from the salt. The role of the plasticizer is to dissociate the salt thereby increasing the number of mobile ions, which lead to conductivity enhancement. The conductivity was calculated using the bulk impedance obtained through impedance spectroscopy. The Cole–Cole plots illustrating the variation of the negative imaginary impedance with the real impedance do not always show the double layer reactance but the plot of dielectric constant ϵ r versus frequency tends to a maximum at low frequencies. The real and imaginary parts of the electrical modulus of samples containing salt show a “long tail” feature, which is not found in the electrical modulus spectra of the unsalted samples. This long tail feature can be attributed to high capacitance, which further supports the plasticizers role as an agent to dissociate the salt into ions.

Chitosan-based electrolyte for secondary lithium cells

The system chitosan : ethylene carbonate : LiCF3SO3 was prepared by the solution cast technique. To verify that the conductivity of the material is due to the salt, the electrical conductivity at room temperature of the chitosan acetate film and that of the chitosan acetate films containing different amounts of ethylene carbonate added to it were measured. The order of magnitude of the electrical conductivity was 10−10 S cm−1. Films containing fixed content of chitosan and plasticizer but different amounts of salt were then prepared in the same manner and the highest electrical conductivity obtained was 1.3 × 10−5 S cm−1 at room temperature. These results indicate that the conductivity is due to the salt. Conductivity-temperature studies show that the ln σ T versus 103/T graphs obey Arrhenius rule implying that the conductivity occurs by way of some thermally assisted mechanism. Polarization current measurement shows that the lithium ion transference number is ∼0.09. A LiMn2O4/chitosan-LiCF3SO3/C cell was fabricated which cycled between 1.5 to 2.5 V with fading capacity. This could be the result of LiF formation due to interaction between the salt and the fluorine in the binding agent.

Electrochemical double layer capacitor based on cellulose-PVA hybrid electrolyte

A polyvinyl alcohol (PVA) cellulose electrolyte was prepared by casting a solution of PVA and H3PO4 on both sides of a cellulose membrane (filter paper). The ionic species H+ are caused by the H3PO4 acid which is entrapped inside the PVA and in the pores of the filter paper. The electrolyte was sandwiched between two carbon electrodes to form an electric double layer capacitor (EDLC). The EDLC exhibits a good charge and discharge characteristics with a capacitance value of 30 Fg−1.