In this paper, the PEO-based composite polymer electrolytes are presented, in which phosphonic acid, methyl-, bis[(5-ethyl-2-methyl-2-oxido-1,3,2-dioxaphosphorinan-5-yl)methyl]ester (middle MW cyclic phosphate) works as both the plasticizer and the flame-retarding additive. The flame-retarding ability of middle MW cyclic phosphate was proved through a designed flammability test. The effect of middle MW cyclic phosphate on the thermal stability of CPEs was demonstrated by thermogravimetry (TG) test. Electrochemical measurements prove that the CPEs containing middle MW cyclic phosphate have a very wide electrochemical stability window at both the room temperature and 80 degrees C, and can be used in lithium batteries with a large choice of redox couples as cathode materials. (c) 2006 Elsevier B.V. All rights reserved.