Among the major thermophysical properties of electrolytes, thermal stability and ionic conductivity are the most two crucial properties in determining the thermal performance of supercapacitors. The former determines the usable temperature range of supercapacitor devices, and the latter dictates the electrochemical performance at different temperatures. This section generally introduces the relationships among the critical thermophysical properties of electrolytes, followed by a discussion of the thermal stability and ionic conductivity of different common electrolytes.