NOVELTY - An ionic liquid composite electrolyte comprises 1,4,6,9-tetraoxa-boraspiro-nonane-2,3,7,8-tetrone and organic compound containing amide functional group. The electrolyte is a full-solid material formed by mixing high molecular material and optionally reduced amount of plasticizer, or gel material formed by mixing the high molecular material and plasticizer. The plasticizer contains carbonic ester, carboxylic ester, sulfurous ester, organic phosphide, silane, ether or low molecular polymer.    USE - Ionic liquid composite electrolyte for use in electrochemical storage system.    ADVANTAGE - The ionic liquid composite electrolyte has excellent thermal stability, electrochemical performance and provides electrochemical storage system having high energy density and improved safety.    DETAILED DESCRIPTION - An ionic liquid composite electrolyte comprises 1,4,6,9-tetraoxa-boraspiro-nonane-2,3,7,8-tetrone and organic compound containing amide functional group. The electrolyte is a full-solid material formed by mixing high molecular material and optionally reduced amount of plasticizer, or gel material formed by mixing the high molecular material and plasticizer. The high molecular material is polyether material obtained using polyoxyethylene as main component, polyelectrolyte modified by doping with salt, plasticizer or fiber, porous polyoxyethylene film, polyelectrolyte containing polyacrylonitrile, polymethacrylate, polyvinylidene fluoride, porous polyvinylidene fluoride phase-inverted film or non-phase inverted film, polypropylene, polythene material or their composite. The plasticizer contains carbonic ester, carboxylic ester, sulfurous ester, organic phosphide, silane, ether or low molecular polymer. The mass ratio of the plasticizer in the solid polymer electrolyte material and in the gel material is 0-5 %mass and 20-80 %mass, respectively. The organic compound containing amide functional group is chosen from formulae: R3-C(=O)-N(-R1)(-R2) (I), R3N(-R4)-C(=O)-N(-R1)(-R2) (II), and organic compounds chosen from formulae (III)-(XII).    R1-R5=single bond, double bond, H, halo, phenyl, trifluoromethyl or optionally substituted alkyl.