A random poly(ethylene-co-acrylic acid) (PE-A) with an acrylic acid (AA) content of 5.0-20mol% was functionalized by esterifying acrylic acid group with poly(ethylene glycol) monomethyl ether. Polyethylene oxide functional groups such as a pendant were introduced into the polyethylene backbone chain. The resulting polymer (PEGM-g-EAA) can be easily formed to a thin sheet and possesses the adhesion property such as gluing. Its thin film could absorb and hold a large quantity of the electrolyte solutions employed for the lithium batteries. The ionic conductivity of the PEGM-g-EAA gel electrolyte obtained with the starting PE-A with acrylic acid content of 9.0 mol% was a value of around 1.5 x 10(-3) S cm(-1) at 20 degrees C. The ionic conductivity results obtained for the network type gel, which was entangled with the present PE-A-based polymer, were 1.1 x 10(-3) S cm(-1) and 5.5 x 10(-3) S cm(-1) at 0 degrees C and 80 degrees C, respectively. The characteristics of good thermostability, transparency and good adhesion to the electrodes have also been demonstrated. As an example, the test cell consisted of the proposed polyolefin gel electrolyte, a LiCoO2 cathode and a lithium anode showed excellent charge/discharge characteristics. (C) 2008 Elsevier B.V. All rights reserved.