SEM). The electrochemical properties of composite electrolyte membranes were studied. The ionic conductivityof the polymer electrolyte composed of 75wt. % 1MLiBF4 in ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:1by weight) was about 2.6×10−3 S cm−1 at ambient temperature. The electrochemical window of the polymer electrolyte was about 4. 6Vdetermined from the linear sweep voltammetry plot. The lithium ion polymer batteries were assembled by sandwiching gel polymer electrolytebetween LiCoO2 cathode and mesophase carbon fibre (MPCF) anode. Charge-discharge test results display that lithium ion batteries withthese gel polymer electrolytes have good electrochemical performance.