The application of composite cathode materials including LiFePO4 (lithium iron phosphate) of olivine crystal structure, which has high thermal stability, were investigated as alternatives for hybrid battery-capacitors with a LiMn2O4 (spinel crystal structure) cathode, which exhibits decreased performance at high temperatures due to Mn-dissolution. However, these composite cathode materials have been shown to have a reduction in capacity by conducting life cycle experiments in which a LiFePO4/activated carbon cell was charged and discharged between 1.0 V and 2.3 V at two temperatures, 25 °C and 60 °C, which caused a degradation of the anode due to the lowered voltage in the anode. To avoid the degradation of the anode, composite cathodes of LiFePO4/LiMn2O4 (50:50 wt%), LiFePO4/activated carbon (50:50 wt%) and LiFePO4/LiNi1/3Co1/3Mn1/3O2 (50:50 wt%) were prepared and the life cycle experiments were conducted on these cells. The composite cathode including LiNi1/3Co1/3Mn1/3O2 of layered crystal structure showed stable voltage behavior. The discharge capacity retention ratio of LiFePO4/LiNi1/3Co1/3Mn1/3O2 was about twice as high as that of a LiFePO4/LiMn2O4 cell at thermal stability experiment for a duration of 1,000 hours charged at 2.3 V and a temperature of 80 °C.