TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The electrolyte solution further contains guanidine thiocyanate and 4-tert-butyl pyridine. The concentration of the alkyl-substituted imidazole iodine compound is 0.1-1 mol/L, preferably 0.2-0.9 mol/L, more preferably 0.2-0.7 mol/L. The concentration of 1-allyl-3-methyl imidazole iodine is 0.1-1 mol/L, preferably 0.2-0.9 mol/L, more preferably 0.2-0.7 mol/L. The concentration of lithium iodide is 0.01-0.2 mol/L, preferably 0.02-0.18 mol/L, more preferably 0.5-0.15 mol/L. The concentration of iodine is 0.01-0.3 mol/L, preferably 0.02-0.28 mol/L, more preferably 0.05-0.25 mol/L. The concentration of guanidine thiocyanate is 0.01-0.2 mol/L, preferably 0.02-0.18 mol/L, more preferably 0.5-0.15 mol/L. The concentration of 4-tert-butyl pyridine is 0.1-2 mol/L, preferably 0.2-1.8 mol/L, more preferably 0.3-0.15 mol/L. Preferred Components: The alkyl-substituted imidazole iodine compound is 1,2-dimethyl-3-propyl imidazole iodine, 1-ethyl-3-methyl imidazole iodine, 1-propyl-3-methyl imidazole iodine, 1-butyl-3-methyl imidazole iodine, 1-hexyl-3-methyl imidazole iodine, 1,3-dimethyl imidazole iodine, 1-octyl-3-methyl imidazole iodine, 1-decatyl-3-methyl imidazole iodine, 1-dodecyl-3-methyl imidazole iodine, 1-hexadecyl-3-methyl imidazole iodine and/or 1-benzyl-3-methyl imidazole iodine, preferably 1,2-dimethyl-3-propyl imidazole iodine. The 4-tert-butyl pyridine is replaceable with N-methyl benzimidazole and/or N-butyl benzimidazole. The solvent is nitrile compound, methanol, ethanol, isopropanol, methyl formate, methyl acetate, ethyl formate, ethyl acetate, ( gamma )-butyrolactone, ( delta )-caprolactone, propene carbonate, N-methylformamide, N,N-dimethylformamide, N-ethylformamide, methyl ether, ethyl ether, dimethoxyethane and/or tetrahydrofuran, preferably 3-methoxypropionitrile. The nitrile compound is chosen from 3-methoxypropionitrile, acetonitrile, valeronitrile, butyronitrile, isobutyronitrile, propionitrile, malononitrile, succinonitrile, and/or their derivatives.