TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Electrolyte Solution: The solvent system is comprised of 100% of carbonate (I). The quaternary ammonium compound is present in the electrolyte solution in a concentration of 0.6-3 M.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The conductive salt includes at least one quaternary ammonium compound (preferably tetraethyl ammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, diethyldimethylammonium tetrafluoroborate, ethyltrimethylammonium tetrafluoroborate, dimethylpyrrolidinium tetrafluoroborate, diethylpyrrolidinium tetrafluoroborate, ethylmethylpyrrolidinium tetrafluoroborate, spiro-(1,1(1))- and/or bipiperidium tetrafluoroborate). The conductive salt is a quaternary ammonium tetrafluoroborate. The conductive salt includes a lithium salt. The solvent (S1) is selected from linear carbonates, cyclic carbonates, carboxylic esters and/or ethers (preferably cyclic carbonates). WIDER DISCLOSURE - Also disclosed as new, are substituted symmetrical or asymmetrical carbonates (I).    SPECIFIC COMPOUNDS - 2 Compounds i.e. Methyl-(2-methoxyethyl)-carbonate (CH3-O-(CH2)2-O-C(=O)-O-CH3) and bis-2-methoxyethyl carbonate ((CH3-O(CH2)2-O)2-C(=O)) are specifically claimed as (I).    EXAMPLE - Into a flask, dimethyl carbonate (DMC) (1749 g, 19.41 moles), 2-methoxy ethanol (246.14 g, 3.24 moles), and 25% sodium methoxide (49.23 g, 5 wt.%) in methanol solution were added. This was stirred at room temperature for 30 minutes until a cloudy, white suspension began to form. This mixture was then heated slowly to 70 degrees C, and methyl-(2-methoxyethyl) carbonate (MMC) and bis-2-methoxy ethyl carbonate (BMC) were collected. The heating was continued until the reaction flask reached to 100 degrees C and the distillation temperature reached 72 degrees C. At this point, the reaction flask contents contained only a small percentage of DMC and no methanol. The reaction mixture was allowed to cool to room temperature. The reaction mixture was treated with NaH2PO4, mixed, and filtered. This step was then repeated with the filtrate to assure that no catalyst remained. After work up, MMC (91% yield, 100% purity) was collected. The remainder of the mixture was composed of 6% MMC and 9% BMC. An electrolyte, diethyl dimethyl ammonium tetrafluoroborate, was dissolved in the mixed solvents containing MMC and BMC to have a concentration of 2 M. The electrolyte exhibited low temperature characteristics without coagulating and good conductivity in a wide temperature range down to -60 degrees C.