Tan Winie

Dielectric behaviour and AC conductivity of LiCF3SO3 doped H-chitosan polymer films

H-chitosan that exhibited solubility in THF was prepared by acyl modification of chitosan. Films of H-chitosan containing LiCF3SO3 were prepared by the solution cast technique. The effect of salt concentration on the frequency-dependent dielectric properties of H-chitosan: LiCF3SO3 complexes were investigated by impedance spectroscopy, in the temperature range from 243 to 373 K. The dielectric properties and ac conductivity of the samples prepared have been analyzed. The dielectric constant increases sharply with temperature in the low frequency region. At higher frequencies, the effect of temperature on the dielectric constant is negligible. The values of dielectric constant were also found to increase with increasing conductivity of the samples. The imaginary part, Mi of electrical modulus shows the formation of dispersion peak. Relaxation times for the ionic charge carriers were extracted from the loss tangent maximum peak at various temperatures. The plot of relaxation times as a function of temperature shows Arrhenius type behaviour. The ac conductivity was found to obey the universal power law and as the temperature increases, the feature of σ(θ) α θn is more predominant. The temperature dependence of the power law exponent n is reasonably interpreted by the overlapping large polaron tunneling (OLPT) model.

Transport studies on filler-doped chitosan based polymer electrolyte

The room temperature conductivity of the chitosan complex containing 40 wt.% of salt increased from 6.02×10−6 Scm−1 to 2.10×10−5 Scm−1 after the addition of 1.0 wt.% aluminosilicate. Conductivity of the electrolyte is contributed from the charge carrier density and ionic mobility. The Rice and Roth model was applied in calculating the mobility, μ and density of ions, n. The number density of ions, n, increases with temperature, while mobility, μ decreases with increasing temperature. This work also suggests that the filler did not change the conduction mechanism of the charge carrier in chitosan-salt-filler complexes but helped to increase the conductivity value of the materials.

Mixed doped lithium nickel vanadate as cathode material by sol–gel and polymer precursor method

Abstract The mixed doped LiNi1−xMnxVO4 (0⩽x⩽1) has been synthesised by using sol–gel and polymer precursor methods. X-ray diffraction, thermogravimetric analysis/differential thermogravimetric analysis and scanning electron microscopy analyses have been carried out to study the structural and physical properties of the samples which can be used as the cathode material for lithium ion batteries. Citric acid was added during the sample preparation as the chelating agent. The prepared samples have been characterised thermally by thermogravimetric analysis/differential thermogravimetric analysis. The analysis shows few endothermic peaks at 80, 301, 371 and 573°C and this is due to the weight loss during the thermal process which corresponds to the inorganic and organic decompositions of the precursor. Scanning electron microscopy images show that the grain size of the composite samples increases with increasing temperature for the sample fired from 500 to 800°C, revealing a spherical shape of grain distribution at low temperature and a polyhedral shape at the highest sintering temperature. The size of the particle synthesised using both methods is also discussed in this work.

Effect of ethylene sulphite on the conductivity and morphology of PEO-KOH films.

The plasticized PEO-KOH films have been investigated using the electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The conductivity of films increased by about 2 orders of magnitude from 10-5 to 10-3 S cm-1 at r.t. on addition of 0.5 wt.% of ethylene sulphite (ES). The degree of crystallinity was calculated from the XRD patterns. SEM micrographs show that the plasticized films were porous. The highest conductivity of plasticized films at r.t. was (1.3 ± 0.2) x 10-3 S cm-1 for the film with 0.5 wt.% of ES content. The number density of mobile ions was shown to increase indicating that ES has dissociated more salts into ions and thereby increasing the conductivity.

Characterization of Plasticized Hexanoyl Chitosan-Based Polymer Electrolytes and Application in LiCoO2/MCMB Cells

Hexanoyl chitosan that exhibited solubility in THF was prepared by acyl modification of chitosan. Films of hexanoyl chitosan-based polymer electrolyte were prepared by the technique of solution casting. The effect of plasticizers on the electrical properties of hexanoyl chitosan: LiCF3SO3 electrolytes have been investigated. The plasticizers used were EC, PC and a mixture of EC and PC. The highest room temperature conductivity of about 1.1 x 10-4 S cm-1 was achieved for electrolyte with composition of 50:50 (wt.%) mixture of PC: EC. The variations in conductivity have been explained using the Rice and Roth model from which the numbers of free ions per unit volume, mobility and diffusion coefficient of free ions were obtained. Electrochemical cells based on LiCoO2/MCMB couple were assembled using the electrolyte that exhibited the highest ionic conductivity. The performance of the cells have been studied and discussed in this paper.