1. Introduction
Solid polymer electrolytes (SPEs) has great potential in electrical energy storage systems such as International Journal of Engineering Advanced Research (IJEAR)
eISSN: 2710-7167 [Vol. 1 No. 4 December 2020]
Journal website: http://myjms.mohe.gov.my/index.php/ijear
DIELECTRIC AND MODULUS FORMALISM STUDIES ON METHYL CELLULOSE BASED POLYMER ELECTROLYTES
Mas Fiza Mustafa1* and Nur Hikamah Seth2
1 2 Centre of Foundation Studies, Universiti Teknologi MARA Selangor, Dengkil Campus, MALAYSIA
*Corresponding author: [email protected]
Article Information:
Article history:
Received date : 13 January 2020 Revised date : 15 January 2020 Accepted date : 6 November 2020 Published date : 7 December 2020
To cite this document:
Mustafa, M., & Seth, N. (2020).
DIELECTRIC AND MODULUS FORMALISM STUDIES ON METHYL CELLULOSE BASED POLYMER ELECTROLYTES. International Journal Of Engineering Advanced Research, 1(4), 10-16.
Abstract: Potassium ion (K+) based solid polymer electrolyte (SPE) and Methylcellulose (MC) as a polymer host has been prepared using solution cast technique with distilled water as solvent. In this study, the film was characterized by impedance spectroscopy to measure its ionic conductivity. The highest ionic conductivity value is 7.23 x 106 S cm-1 for MC-KOH polymer at ambient.
Dielectric data were analysed using complex permittivity and complex electrical modulus for the sample with highest conductivity. Dielectric data proved that the increase in conductivity is mainly due to the increase in number of charge carriers.
Keywords: methyl cellulose, alkaline battery, potassium hydroxide, dielectric constant.
2. Literature Review
In this study, methylcellulose which is a polymer that has high biodegradability properties and low cost was studied to be added with potassium hydroxide as the alkaline salt. The ionic conductivity at room temperature was reported to be 7.23 x 10-6 Scm-1 [8]. Despite the increment of ionic conductivity in alkaline salt, it is still low if it were to compare with other polymer electrolyte.
Hence, the ionic conductivity value needs to enhance in order to fulfil the needs of the market. The plasticization method is a promising method to modify the SPE. It involves the introduction of plasticiser into SPEs system which also known as gel polymer electrolytes (GPEs). Several plasticiser such as propylene carbonate (PC), and ethylene carbonate (EC) are widely used in polymer electrolyte [10][15]. Electrical conduction in polymers has been studied aiming to understand the origin and nature of charge transport prevalent in these materials. These parameters are related to the chemical composition, microstructure, and morphology of the material [2][16].
Steady-state current measurements are necessary to apply due to the existence of absorption current. The absorption currents are generally observed in bulk insulating materials [3] hence, currents were measured after a period, which depend on both temperature and electric field.
The degree of electrical polarization a material experiences under the influence on an external electric field can be diagnose through its dielectric permittivity. The dielectric permittivity is a function of frequency because of various relaxation processes. Hence, frequency dependence of dielectric permittivity is a study to give an idea of various dielectric processes of the system. In order to understand more on the ion transport behaviour and to obtain the information of ionic and molecular interaction in the solid polymer electrolyte, the study of dielectric phenomenon is important and become crucial.
This paper reported the dielectric permittivity to look at the relaxation processes that can be seen in MC-based polymer electrolyte from the study of frequency and temperature dependence of dielectric behavior.
2. Method
Methylcellulose (MC) solution doped with various amount of potassium hydroxide (KOH) as the ionic dopant were prepared by solution casting technique. 0.5 g of methylcellulose was dissolved in 25 ml distilled water. An amount of 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% of KOH was added into the solution and stirred until the solution becomes homogenous. Then, the solution was casted onto petri dish and left to dry at room temperature before further analysis.
2.1 Measurement
The conductivity of the sample was measured by using Impedance spectroscopy interfaced to a computer. The impedance values were measured in the frequency range of 50Hz to 1 MHz at ambient temperature. The plot of imaginary impedance, Zi versus real impedance, Zr was observed and the bulk resistance, Rb could be obtained. Hence, the ionic conductivity of the sample at room temperature can be calculated by using equation (1):
σ = t / Rb A (1)
Where Rb is bulk resistance, t is the thickness of the thin film and A is the surface area of contact.
Figure 1: Variation of ionic conductivity versus wt% KOH for the polymer electrolyte system.
3. Results and Discussion
The complex impedance plot generated by impedance measurement consist of (i) a title spiked, (ii) a depressed semicircle or (iii) a combination of depressed semicircle and title spike [7].
1.00E-10 1.00E-09 1.00E-08 1.00E-07 1.00E-06 1.00E-05 1.00E-04
0 10 20 30 40 50 60
Conductivity σ, (Scm-1)
wt% KOH
I II III
conductivity value decreases in addition of more that 30 wt% of KOH into MC system. This might be due to the accumulation of ion cluster which provides an overcrowded ions environment in the polymer system [4].
In order to describe the conductivity behavior of polymer electrolytes, the dielectric properties of the system was studied. In polymer electrolytes, ions are the charge carriers where the dielectric constant represent the stored charge in the material [1]. The dielectric constant is directly proportional to the dissociation energy. When the dielectric constant increases, the number of charge carriers increases as well [11].
Figure 2 (a) and (b) shows the real part, Er and imaginary part, Ei of dielectric constant at selected wt% of ionic dopant content. It can be observed from the graph that the real part of dielectric constant, Er increases with increasing ionic dopant content until 30 wt% and then decreases when more ionic dopant being added into the system. The decrease of dielectric constant after addition of more than 30 wt% KOH might be due to the strong dipole moment, which could facilitate the stiffening of the MC chains causing a decrease in the local conductivity at the interface of the polymer matrix [5].
Figure 2 (a) Real part of dielectric constant as a function of frequency for selected samples.
Figure 2 (b) Imaginary part of dielectric constant as a function of frequency for selected samples.
In order to understand the dielectric behaviour, dielectric moduli is needed to suppress the effects of electrode polarization. The real and imaginary parts of the modulus approach zero at low frequency region indicate that the electrode polarization phenomenon makes a negligible contribution. The large capacitance associated with the electrodes results in the long tail at lower frequencies region. It is observed that the presence of a peak at higher frequency for the polymer electrolytes system, which indicates that ionic conduction, is predominant in the polymer electrolytes system.
Figure 3 (b) Imaginary part of electric modulus as a function of frequency for selected samples.
5. Conclusion
The addition of 30 wt% potassium hydroxide as ionic dopant into methylcellulose solution has increased the ionic conductivity of the polymer electrolytes with maximum conductivity of 7.23 x 10-6 Scm-1. The number of charge carriers influences the increase in ionic conductivity of the system that can be observe from the dielectric behavior.
6. Acknowledgement
The authors would like to thank the Institute Pengurusan Penyelidikan dan Inovasi (IRMI) UiTM for supporting this research under Geran Penyelidikan Lestari 2017, 600-RMI/MyRA 5/3/LESTARI (078/2017).
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