NOVELTY - A composite gel polymer electrolyte film comprises 1-10 wt.% lithium-containing silica, 30-48 wt.% polyvinylidene fluoride (PVDF) having a molecular weight 5x 105, and 50-61 wt.% 1M lithium hexafluorophosphate carbonate electrolyte. The film has a thickness of 30-50 mu m.    USE - Composite gel polymer electrolyte film used for lithium ion battery.    ADVANTAGE - The film has ionic conductivity thin film of 3.87x 10-2 S-cm-1 at 30 degrees C, and electrochemical window that reaches 5.1 V.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for preparation of composite gel polymer electrolyte film comprising: (A) taking tetraethyl orthosilicate and KH560 (RTM: glycidyloxypropyl-trimethoxy silane) at a mol ratio of 3:1-1:2, where the catalyst is hydrochloric acid, adjusting the pH value to 2-4, raising the temperature to 65-75 degrees C, reacting for 5-8 hours to form a modified silica sol, and reacting for 1-2 hours to obtain lithium-containing silica sol; (B) preparing a lithium-containing silica sol doped PVDF composite porous film with molecular weight of 5x 105, dissolving PVDF powder in N,N-dimethyl formamide solution (DMF) at room temperature, stirring at room temperature for 12-24 hours, adding the lithium-containing silica sol from step (A) and stirring for 6-12 hours, completely dissolving, where solution concentration is 0.15 g/ml, controlling the thickness at 30-50 mu m, and then precipitating with methanol using an immersion precipitation method to prepare lithium-containing silica sol doped PVDF composite porous membrane; and (C) preparing a lithium-containing silica sol doped PVDF composite gel polymer electrolyte film to obtain the lithium-containing silica sol doped PVDF composite porous membrane, vacuum drying for 8-12 hours, and soaking liquid electrolyte for 0.5-1 hour in the glove box to obtain the film having a thickness of 30-50 mu m at 80-100 degrees C of lithium-containing silica sol doped PVDF composite gel polymer electrolyte film.