International Journal of Material Science
IJMS
TABLE-2 BATTERIES PARAMETERS OF NANO COMPOSITE POLYMER ELECTROLYTES Solid State rechargeable battery parameters
OCV (Volt)
Current (I) (µA)
[93PEO-7NH4SCN]:1% Mg-Zn ferrite
1.57
1.4
Electric Power (P) (µW) 1.69
σac=σo+Aωn (6) Where, σo is the dc conductivity (extrapolation of the platue region to zero frequency gives the d. c. ionic conductivity), A the pre-exponential factor and n the fraction exponent laying between 0&1. The calculated value of conductivity for the best conducting electrolyte i.e. [93PEO7NH4SCN]: 1% Mg-Zn ferrite composition is σo = 9.0x10-5 S/cm, and n=1. The change in a. c. conductivity is not prominently observed with applied frequency. This means that the charge carriers are not sufficiently free to follow the changing electric field and therefore conductivity remains nearly frequency independent. Figure -11(b) shows the variation of a. c. conductivity against frequency and temperature for [93PEO-7NH4SCN]: 1% Mg-Zn ferrite. In NCPEs a.c., conductivity increases linearly with frequency and temperature.
Electric energy (E) (µWh) 2.53
Current density (J) (µAcm-2) 0.71
Power density (µW/Kg)
Energy density (µWh/Kg)
670
1003
In order to study the physical mechanism of the induced dielectric constant, the frequency dependence of the dielectric constant (ε’), imaginary part of dielectric permittivity (ε″) and a.c. conductivity at room temperature were plotted as figure12. Dielectric constant (ε’) exhibits asymptotic drop with increasing frequency. Further the slope of ε″ vs. frequency is found to be near (-1) in low frequency range. The dielectric loss tanδ ( as given in fig-8) mainly consists of two contributions one from the dielectric polarization process tanδrelax. and other from d.c. conduction tanδdc. So tanδac can be expressed as, tanδac=σdcωε (7) Where ω =2πf equation (7) can be rewritten as ε″dc= σdc /ω . This means that the slope of log ε″dc vs log ω (or log f) is -1. This slope (-1) indicates that the predominant dc contribution in the studied nanocomposite polymer electrolyte system [33, 34]. Once of the basic requirements of these entire polymer electrolytes is high ionic conductivity over a wide temperature window to establish their worth in electrochemical devices. Thus, besides structural, thermal and electrochemical characterizations, electrical characterization of NCPE is yet another important factor. Keeping this in mind electrical characterization on the developed nanocomposite polymer electrolytes was pursued.
Figure 12: Frequency dependence of the ε’, ε” and ac conductivity for[93PEO-7NH4SCN]: 1% Mg-Zn ferrite system. Figure 11 (a): Variation of ac conductivity with frequency for different composition of nano polymer composite electrolytes at ambient temperature. (b):Variation of ac conductivity with frequency for [93PEO-7 NH4SCN]: 1% Mg-Zn ferrite at different temperature.
The performance of a battery is evaluated from the cell parameters [35-37]. Various related parameters on the batteries based on NCPE were estimated. The open circuit voltage (OCV) of fabricated were noted using high resolution multimeter and were found to be 1.57 V of Mg-Zn ferrite
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