NOVELTY - Modified silica is obtained by dispersing silica in anhydrous organic solvent, stirring, adding cross-linking segmented copolymer, hydrochloric acid and water, reacting for 10-48 hours at 20-30 degrees C, centrifugally washing the reaction product, and vacuum drying. The modified silica has grain diameter of 50-500 nm. The content of copolymer is 5-50 %mass with respect to silica. The cross-linking segmented copolymer is formed by polymerizing specific monomers.    USE - Modified silica is used for diaphragm of high-performance lithium ion battery (all claimed).    ADVANTAGE - The modified silica provides diaphragm having excellent rupture strength and elongation property.    DETAILED DESCRIPTION - Modified silica is obtained by dispersing silica in anhydrous organic solvent, stirring, adding cross-linking segmented copolymer, hydrochloric acid-tetrahydrofuran and water, reacting for 10-48 hours at 20-30 degrees C, centrifugally washing the reaction product, and vacuum drying. The modified silica has grain diameter of 50-500 nm. The content of copolymer is 5-50 %mass with respect to silica. The cross-linking segmented copolymer is formed by polymerizing monomers (A,B'), and is of formula (I).    m,n=5-500;    A=cinnamon ethyl acrylate, hydroxyethyl methacrylate, methyl methacrylate, ethyl cinnamate, methacrylonitrile acyloxy propyl trimethoxy silane or methacryloyl oxy propyl isopropoxy silane;and    B'=methyl methacrylate, ethyl methacrylate, butyl acrylate, tert-butyl acrylate, butyl methacrylate, tert-butyl methacrylate, propylene silicon ethylene oxide, maleic anhydride or methyl acrylate.    An INDEPENDENT CLAIM is included for high-performance lithium ion battery diaphragm, which is obtained by mixing modified silica with high molecular weight polyolefin, melting, extruding, forming film with hard elastic structure, continuously stretching, and thermally shaping at 0-200 degrees C. The polyolefin is homopolymer or copolymer of alpha -olefin, which is chosen from ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-decene, 1-dodecene, 4-methyl-1-pentene and 3-methyl-1-pentene. The intrinsic viscosity of polyolefin is 0.5-40 dL/g.