The composite polymer gel electrolytes (CPGE) for lithium-ion batteries are prepared by combining poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and hydroxypropylcellulose (HPC) as binary polymer components, Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) as an inorganic filler, and 1 M LiPF₆ dissolved in EC:PC:EMC as an electrolyte solution. The PVdF-HFP is included as a linear flexible polymer chain in the electrolyte medium, the rigid rod-like molecules of HPC has the lyotropic property between liquid crystalline and isotropic phases, and the LATP supports mechanical strength and also provides another conduction path in the gel medium [1] to increase ionic conductivity. The synergy among each component is expected to lead highly ionic conductive electrolytes with excellent mechanical strength. In this study, the electrochemical properties of LATP-filled CPGE are investigated and the charge-discharge performance of LiCoO₂/graphite lithium-ion battery cell adopting the CPGE is also carried out. Through such the electrochemical investigations, the optimum amount of LATP showing the best performance would be mainly determined. Moreover, the low-temperature performance of the LiCoO₂/CPGE/graphite cell would be particularly examined because the LATP(50 wt.)-filled CPGE (polymer 100 wt.) exhibits higher ionic conductivity (e.g., 4x10^-3 S/cm) at low temperature (e.g., -10^oC), compared with the CPGE without LATP (3.6x10^-4 S/cm). In the presentation, how each component and its content contribute to the electrochemical performance of the cell would also be discussed in detail.