A high lithium ion conductivity polymer electrolyte with excellent mechanical properties was developed in a polyolefin hard segment with a polyethylene oxide conducting phase block copolymer (OEO) and tetraethylene glycol dimethyl ether (G4) composite polymer with lithium bis(fluorosulfonyl)imide (LiFSI). The effect of the modulus of polymers on the ionic conductivity is generally controversial; high ion conducting polymer electrolyte typically exhibit poor mechanical properties. The composite polymer electrolytes developed in this study have ion conductivities in the range of 10(-5) to 4 x 10(-4) S cm(-1) and tensile strengths in the range of 1 to 12 MPa at room temperature. 10OEO-1.4LiFSI-2.5G4 where OEO is based on ethylene oxide (EO) units, has ionic conductivity of 13 x 10(-4) S cm(-1) and tensile strength of 5.1 MPa at room temperature. The high G4 content composite of 10OEO-3.0LiFSI-4.0G4 has a high ion conductivity of 4.0 x 10(-4) S cm(-1), but a low tensile strength of 1.0 MPa at room temperature. The OEO-LiFSI-G4 composite polymer with high conductivity and high tensile strength is an attractive candidate for the electrolyte in lithium polymer batteries. (C) 2016 Elsevier B.V. All rights reserved.