Enhancement of ionic conductivity in polyacrylamide based polymer electrolytes for tin-air batteries

The purpose of this research is to study the ionic conductivities of gel polymer electrolytes (GPEs) and composite solid polymer electrolytes (CSPEs) for tin-air battery application based on polyacrylamide as host polymer. Methanesulfonic acid and p-toluenesulfonic acid were used as additives. Electrochemical impedance spectroscopy (EIS) was used to measure the ionic conductivities of the samples by using the bulk electrolyte resistance values (Rb). The FTIR spectra were analyzed to describe the mechanism involved in the proton transfer within the membranes by referring to the characteristic shifts of the absorbance bands of C=O and N-H2. Tin-air batteries, with a configuration of Sn(anode)/GPE/ air(cathode) were fabricated to study the electrochemical properties of the GPEs. The batteries were discharged at various constant of current densities. The results showed that the maximum ionic conductivities of 7.0 x 10-1 S/cm and 9.34 x 10-1 S/cm were obtained for GPEs at a loading of 3.0 M MSA and 5.0 M of pTSA respectively. The highest ionic conductivity of 1.17 x 10-6 S/cm and 4.45 x 10-5 S/cm were observed at 5.0 M and 4.0 M loading of MSA and pTSA into CSPEs. The FTIR spectra indicated that the proton transfer in GPEs occurred through the protonation of NH2 group of PAAm. Whereas, in CSPEs the protons were transferred from sulfonic acid to the fuctional group of C=O of PAAm through the formation of hydrogen bond. The OCV exhibited by tin-air cell of PAAm-MSA GPE was 1.27 V compared to 1.23 V for cell with PAAm-pTSA GPE. The tin anode of the cell for PAAm-MSA GPEs produced an average specific discharge capacity of 456mAh/g, while for PAAm-pTSA GPEs was 439 mAh/g. The tin-air cell of PAAm-MSA GPEs also supported a relatively high current of 12 mA/cm2 with a maximum power density of 5.25 mW/cm2. In conclusion, the research showed that MSA and pTSA as additives the enhanced the ionic conductivity of the PAAm electrolytes. The mechanism involved in the proton transfer of GPEs different from the mechanism in CSPEs. The tinair battery cell with PAAm-MSA GPE exhibited superior electrochemical cell performance in the discharge capacity. Thus, this research proves that PAA-MSA GPEs have high potential for application as tin-air battery.