Electrical, structural, and thermal properties of succinonitrile-LiI-I2 redox-mediator

We synthesized a solid I−/I3−-based redox-couple electrolyte using a mixture of succinonitrile, LiI and I2. An increase of LiI to succinonitrile mole ratio (x) up to 2.5% led to a fast rise in the electrical conductivity (σ25°C) of the electrolytes. Further increase in x slowly increased the σ25°C-value. The composition with x = 5% achieved the highest σ25°C-value (~1.6 × 10−3 S cm−1) and was referred to as the optimum conducting composition (OCC) of the electrolytes. Also, an increase of x led to a decrease of the melting temperature of the electrolytes as suggested by the logσ − T−1 study and ascertained by the differential scanning calorimetry study. The logσ − T−1 study showed a linear trend before and after the melting temperature, and the activation energy increased with increasing x-value. The electrical and thermal properties were explained using the vibrational spectroscopy study. The ionic transference number measurement showed that the electrolytes with x = 4 and 5% are predominantly ionic in nature.