Roles of Hydrogen Bonds in Ionic Conductivity in the LiNO₃–Poly(vinyl alcohol) Electrolyte: A Real-Time Raman Spectroscopic Study

The real-time correlation between the ionic conductivity and water structure of the LiNO₃-poly(vinyl alcohol) (PVA) polymer electrolyte was examined. It was found that ionic conductivity decays proportionally with the water content within the system. Under 45% relative humidity (RH) storage conditions, the ionic conductivity of LiNO₃–PVA plateaus at 18 ± 2 mS cm^–1, and under 15% RH conditions, it ranges from 1 to 3 mS cm^–1. Using Raman spectroscopy to track the changes in hydrogen bonding within both liquid and polymer electrolytes, the HOH band (3000–3800 cm^–1) was monitored in real time and compared with the changes in ionic conductivity from the electrochemical cells. The strength of the hydrogen bonding decreased with the increase in LiNO₃ concentration, with little influence from PVA. The specific compositions of the polymer electrolytes were correlated to the equivalent liquid concentrations of LiNO₃. An equivalency of 5–7 M LiNO₃ for 50 wt % water of LiNO₃–PVA was established, resulting in a high ionic conductivity of 48 ± 5 mS cm^–1. The degradation in ionic conductivity can be attributed to fewer hopping sites through bulk water and fewer mobile ions. This analysis provides a simple and reliable method for assessing the performance of the LiNO₃–PVA system, which can be applied to enhance and predict the longevity of other aqueous-based electrolytes.