NOVELTY - Preparation of polymer lithium ion battery involves forming modified septum by mixing chemical crosslinker monomer of high boiling point with polymer with physical cross-linking at weight ratio of 0:100-50:50, and dissolving in volatile organic solvent to form modified solution; forming anode and cathode pole pieces by adding chemical crosslinker monomer in anode and cathode slurries; packaging using modified septum, anode pole piece and cathode pole piece to form electric core, and pouring electrolyte of liquid lithium ion battery into the core; and battery solidifying.    USE - Method for preparing polymer lithium ion battery.    ADVANTAGE - The method uses production procedure and production equipment of liquid lithium ion battery. It provides mass production of polymer battery. The resulting polymer lithium ion battery possesses almost the same electrical property with liquid battery.    DETAILED DESCRIPTION - Preparation of polymer lithium ion battery involves:    (A) forming modified septum by mixing chemical crosslinker monomer of high boiling point with polymer with physical cross-linking at a weight ratio of 0:100-50:50, dissolving in volatile organic solvent to form modified solution having a viscosity of 30-300 psi, dipping liquid lithium ion battery septum as septum substrate in the modified solution, and drying to obtain modified septum;    (B) forming anode and cathode pole pieces by adding chemical crosslinker monomer (0.01-1 wt.%) in anode and cathode slurries used by preparing liquid lithium ion battery, and preparing anode and cathode pole pieces based on pole piece production of liquid lithium ion battery;    (C) packaging by using modified septum, anode pole piece and cathode pole piece to form electric core, and packaging outer package shell;    (D) pouring electrolyte of liquid lithium ion battery comprising thermal initiator in the electric core; and    (E) battery solidifying by sealing the battery obtained after pouring electrolyte in vacuum, solidifying at 60-100 degrees C, anode, septum and cathode in battery to obtain polymer lithium ion battery.    An INDEPENDENT CLAIM is included for a polymer lithium ion battery obtained by the above method.