The performance of natural graphite-fibers/PEO-based gel electrolyte/LiFePO4 cells (7mAh, 4cm2) is reported. The gel polymer electrolytes were produced by electron-beam irradiation and then soaked in a liquid electrolyte. The natural graphite-fiber composite anode in gel electrolyte containing 1.5M LiFSI-EC/GBL (1:3) exhibited high reversible capacity (361mAhg−1) and high Coulombic efficiency (92%). The LiFePO4 cathode in the same gel polymer exhibited a reversible capacity of 161mAhg−1 and 93% Coulombic efficiency. A 1.5M solution of LiFSI in ethylene carbonate (EC)/γ-butyrolactone (GBL) (1:3, v/v) mixed solvent is advantageous for use as the electrolyte in the laminated film bag because of its high flame point (135°C), high boiling point (219°C), low vapor pressure and high conductivity (10.2mScm−1 at 20°C). The Li-ion gel polymer battery shows a very low capacity fade of 5% after 500cycles and also has high-rate capability. The Li-ion gel polymer cell using LiFePO4 cathodes is suitable for HEV applications.