This work presents the development of the electrolyte, ensuring stable operation of the supercapacitors (SC) in a wide temperature range from −60 °C to +60 °C and suitable for commercialization. SC cells based on this electrolyte have high cyclic stability of capacitance at +60 °C and provide high discharge current after a long dwelling time in a charged state at −60 °C. We have investigated electrochemical characteristics of SC based on various electrolyte mixtures optimized with co-solvents such as ethyl acetate, propyl acetate, and butyl acetate in a temperature range from −60 to +60 °C. Methyl triethylammonium tetrafluoroborate (CH3)(C2H5)3NBF4 (TEMA∙TFB) in various concentrations (0.7–1.2 M) was used as a basic salt for measurements. According to electrochemical impedance spectroscopy data, the time constant values grows with an increase of ethyl acetate concentration. We found that cells based on electrolyte, containing 30 vol% ethyl acetate and 1.2 M TEMA TFB, provides optimal capacitive behavior of SCs with the high-performance features in a wide temperature range from −60 up to +60 °C. The capacitance of SC based on the developed electrolytes at −60 °C differs from the corresponding values at room temperature by no more than 10%.