The Role of Ion Hydration in the Performance of Li2SO4-Polyacrylamide Electrolyte Systems: Material Characterizations under Real-Time Conditions

摘要

Li2SO4-polyacryalamide (PAM) neutral pH polymer electrolytes with different salt:polymer molar ratios (5000:1 and 10000:1) were characterized for their ionic conductivity and material properties. Their ionic conductivity over time showed different trends: Li2SO4-PAM(5000:1) increased while Li2SO4-PAM(10000:1) decreased. Materials characterizations of the freestanding films were conducted to identify the cause of the difference in conductivity trends. X-ray diffraction and IR spectroscopy suggested slight differences in film crystallinity and sulfate ion bonding structure, but they were not conclusive. Raman spectroscopy proved to be a better tool as it revealed distinct characteristic peaks for different sulfate ion and water interactions. To correlate the film properties with electrolyte performance, a real-time tracking technique to correlate ionic conductivity and the vibrational spectroscopic responses was developed. Leveraging this approach, the level of hydration surrounding the salt molecule was identified as the determining factor of ionic conductivity in this polymer system. This approach can be extended to predict the shelf and service life of this Li2SO4-PAM system and to optimize the next generations of electrolytes.