TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The carbonate is selected from ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC) and/or methyl propyl carbonate (MPC). The linear saturated ester is selected from methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, butyl propionate, and/or methyl pivalate. The linear saturated ester is included in the content of 10-90 pbw, based on 100 parts by weight of the carbonate.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The compound (C2) having at least two double bonds at an end is a compound having at least two (meth)acrylate groups or vinyl groups at its end. The compound (C2) is a compound of a formula (I). The compound (C2) is tetraethylene glycol diacrylate, polyethylene glycol diacrylate having a molecular weight of 50-20000, 1,4-butanediol diacrylate, 1,6-hexandiol diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate, dipentaerythritol pentaacrylate, and/or dipentaerythritol hexaacrylate. The compound (C2) is included in the content of 0.5-10 parts by weight (pbw), based on 100 parts by weight of the gel polymer electrolyte composition (C1).A=1-12C alkylene or 1-12C haloalkylene;a and m=0-30;B1=H or methyl;b=2-6;X=-CH2-O-(CH2-CH2-O)2-CH2-, -(CH2)m-, C, CE1, -C(E1)(E2)-, -C(E1)(E2)(E3), -C-CH2-O-CH2-C-, -C(E1)-CH2-O-H2-CH2-C-, -C(E1)(E2)-CH2-O-H2-CH2-C-, -C(E1)-CH2-O-CH2-C(E1), -C(E1)(E2)-CH2-O-CH2-C(E3), -C(E1)(E2)-CH2-O-CH2-C(E3)(E4);E1-E4=hydrogen, 1-12C alkyl, 1-12C haloalkyl, or 1-12C hydroxyalkyl.Preferred Process: The gel polymer electrolyte is formed by in-situ polymerization of the gel polymer electrolyte composition (C1) inside an electrochemical device under an inert condition. EXAMPLE - An electrolyte (A1) of 1M concentration was prepared by dissolving lithium hexafluorophosphate (LiPF6) into an electrolyte solvent with a composition of ethylene carbonate and ethyl propionate in 2:1 volume ratio. A gel polymer electrolyte composition comprising (parts by weight (pbw)): the electrolyte (A1), dipentaerythritol penta acrylate having five acrylate groups (2) as a monomer for forming gel polymer by polymerization, and t-butyl peroxy-2-ethyl-hexanoate (0.04) as a polymerization initiator, was prepared.