The successful design of safer electrical energy storage devices must include the use of thermally stable, non-flammable, conductive electrolytes that perform at ambient temperatures as well as at higher temperatures [1-2]. Here, we report the synthesis of three glycerol carbonate (GlyC) solvents for use as electrolytes when combined with 1.0 M LITFSI in high voltage Li ion supercapacitors (LICs). The butyl, benzyl and ethyl glycerol carbonate (GlyC) solvents are non-flammable and stable up to > 125 ^oC. Conductivity is dependent on temperature and of the three solvents, the butyl glycerol carbonate solvent with 1.0 M LiTFSI exhibits the highest conductivity (4 mS/cm). The electrochemical performance and rate capability of the devices, prepared with each of the three electrolytes, were evaluated at room temperatures and at 100 ^oC. The butyl glycerol carbonate electrolyte allows safe operation at 100 ^oC with a notable specific capacitance of 115-162 Fg^-1 as well as room temperature operation with a specific capacitance of 29 Fg^-1. This finding is further supported by the observation of a 40 times increase in ionic conductivity at low temperatures by changing the side chain in the back bone of the glycerol carbonate from benzyl and ethyl to butyl leading to a significant improvement of the electrochemical performance (Figure 1).

References:

1- M. Salari, B. G. Cooper, H. Zhang, and M. W. Grinstaff, Synthesis of an Environmentally Friendly Alkyl Carbonate Electrolyte Based on Glycerol for Lithium-Ion Supercapacitor Operation at 100 °C. Advanced Sustainable Systems, 2017. 1(8): p. 1700067-n/a

2- X. Lin, M. Salari, L. M. R. Arava, P. M. Ajayan, M. W. Grinstaff, Chemical Society Reviews 2016, DOI: 10.1039/C6CS00012F.

Figure 1. (a) Ionic conductivity Profile as a function of temperature for synthesized carbonate solvents containing 1.0M LiTFSI. (b) Comparison of CV obtained for the synthesized electrolytes operated at 100 ^oC and a scan rate of 1000 mVs^-1, demonstrating high temperature performance and rate capability of the synthesized glycerol carbonates.