NOVELTY - An electrolyte additive comprises 4-benzyl-biphenyl compound (I).    USE - Electrolyte additive for manufacturing gel polymer cell (claimed).    ADVANTAGE - The electrolyte additive provides gel polymer cell having high stability, mechanical strength and electrical conductivity.    DETAILED DESCRIPTION - An electrolyte additive comprises 4-benzyl-biphenyl compound of formula (I).    R=methyl or H;    X, Y1=methoxy, H or methyl;and    n=1-10.    An INDEPENDENT CLAIM is also included for a method for applying polymer electrolyte additive which involves obtaining a gel polymer cell including a positive electrode, a negative electrode, separator, electrolyte, the positive electrode comprises a metal current collector, a conductive agent, a binder and 90-97 wt.% lithium transition metal composite oxide as a positive electrode active material, the conductive agent is carbon black and/or conductive graphite, the binder is PVDF, the negative electrode comprises a metal current collector, 90-97 wt.% lithium alloy as a negative electrode active material, a conductive agent, a binder, carbon, petroleum coke , activated carbon, graphite, carbon fibers and/or carbon nanotubes, the conductive agent is carbon black and/or conductive graphite, the binder is PVDF, carboxy methyl cellulose and/or styrene-butadiene rubber, the separator is a polyolefin microporous membrane, the electrolyte comprises an 0.002-0.6 wt.% initiator, film-forming additive and electrolyte solvent, the initiator is benzoyl peroxide, acetyl peroxide, di-tert butyl peroxide, azobisisobutyronitrile or azobis heptanenitrile, the monomer is polyethylene glycol diacrylate, polyethylene glycol methyl acrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate or dipentaerythritol pentaacrylate, the electrolyte solvent is ethylene carbonate, propylene carbonate, butylene carbonate, alpha -butyrolactone, alpha -valerolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, diethyl ethane and/or 1,3-dioxolane, film-forming additive is vinylene carbonate and/or propylene sulfite.