Synthesis and characterization of PEO complexed with NaClO4 soluble base salt and Nb2O5 Nano-filler
Abstract
Conducting solid phase polymer electrolyte (SPE) films were synthesized using solution casting method. The polyethylene oxide [PEO] complexed with an alkali salt sodium perchlorate [NaClO4] and nano-filler Nb2O5 with varying weight percentile [5%-15%] ratios. The complexation of NaClO4 salt with the polymer matrix PEO has been confirmed by XRD and surface morphology was understood by the SEM images and elemental composition was estimated by EDAX results. The AC conductivity measurements were done in the temperature range of 303K–343K using AC conductivity set up. The electrical conductivity shows an improvement and enhanced to fourth order. The conductivity in polymer electrolyte system is due to ions of alkaline salts and Nb2O5 nano-filler which are present in polymer matrix. Several electrical and dielectric characterizations were done for these films.
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Introduction
Solid polymer electrolytes [SPE], also named as ionic conductive polymers, make up of a new case of solid electrolytes, which have been intensively examined and developed since 1970s. In 1973, Wright [1,2] firstly described that polyethylene oxide (PEO)/salts complexes showed ionic conductivity concept. In 1979, Armand [3] claimed that the conductivity of PEO/salts complexes could achieve the order of 10−5 S cm−1 at 303K to 343K of temperature range. Most prominent alkali metal ions, for which polymer electrolytes have been originated, are Li+ and Na+ ions. In the present paper, we have discussed about PEO-NaClO4 polymer-salt electrolyte complex where the conductivity is due to Na+ion conduction. Earlier studies on Na+ ion conducting polymeric electrolytes were on PEO complexes with NaPF6[4], NaSCN, NaI and NaCF3SO3[57]. These electrolytes are utilized in solid state rechargeable sodium batteries [8,9]. It has been shown that PEO-NaClO4 electrolyte is a Na+ ion conducting polymer along with a partial contribution from anionic conduction. In order to improve the conductivity of PEO based electrolytes, at lower operating temperatures, researchers made many strategies to integrate a variety of nano-scale inorganic fillers such as SiO2[10], Al2O3[11], TiO2[12], ZnO[13], ZrO2[14] and CeO2[15] CuO[16] without affecting the other physical properties like mechanical stability, electrolyte reactivity towards electrode etc.,[17-20].
In the present study a systematic effort has been made to prepare and characterize the polymer electrolyte system (Consists of PEO as polymer) composed of sodium perchlorate (NaClO4) as salt and Nb2O5 at 5, 10, 15Wt. % as nano-filler. The electrical conductivity of the polymer/salt complex films at 5 Wt.% of Nb2O5 concentration has been measured and found that the conductivity is maximum and also identified 5 wt% as an optimum conducting composition (OCC) of the Nb2O5 composite polymer electrolyte when compared to 10Wt.% and 15 Wt.% of Nb2O5. In this study, a systematic approach has been made to characterize by studying composition, structure, morphological, and electrical properties of the PEO-NaClO4Nb2O5 Nanocomposite polymer electrolyte (NCPE).
Conclusion
PEO-NaClO4-Nb2O5 polymer-salt with nano-filler complex thin films were synthesized by solution-cast technique with three (5, 10, 15 wt.%) Nb2O5 varying concentrations. Structure and grain size of the films were studied and estimated as 46.06 nm, 46.63 nm and 52.67 nm respectively. Surface morphology was analyzed by SEM and elemental confirmation analysis was done by EDAX and found that all the films were nearly stoichiometric. As an application part the electrical conductivity and dielectric studies were done for the same respective samples. The plot of log conductivity against reciprocal temperature obeys Arrhenius rule. The ionic conductivity range of samples collection was found to be enhanced from 1.874 x 10-5 S/cm to 7.55754 x 10-4 S/cm by increase in temperature from room temperature to 343 K. Hence 5 Wt.% Nb2O5 nano-particles to polymer-salt composite can be treated as an optimized conducting composite (OCC). Calculated activation energy [Ea] from the Arrhenius plots was found to be 0.189 eV. The dielectric constant and dielectric loss were found to decrease with increase in frequency.