Carbon nanotubes (CNTs) are promising conductive additives for lithium-ion polymer (LiPo) batteries. The performance of lithium metal oxide cathodes is highly dependent on the properties of the conductive carbon additive. This study investigates the advantages of CNTs over conventional carbon black for this application. Material properties, including hardness, tensile strength, thermal conductivity, and electrical resistivity, were analyzed and compared using Ansys Granta (CES EduPack 2024 R2) software. The results demonstrate that CNTs are superior in tensile strength (110 MPa), hardness (50 HV), and thermal conductivity (210 W/m·°C). These properties enhance the mechanical integrity of the CNT-based cathode composite, leading to improved battery performance. Furthermore, the electrochemical behavior of CNT/LiNi0.5Co0.2Mn0.3O2 composite cathodes was investigated, focusing on the carbon precursor (methane vs. natural gas) and CNT diameter. At a current rate of 3 °C, multi-walled carbon nanotubes (MWCNTs) derived from methane delivered a specific capacity 20 mAh/g higher than those derived from natural gas. This indicates that methane-derived MWCNTs exhibit superior electrochemical performance, which is attributed to reduced polarization and a higher discharge potential. The study also revealed that MWCNTs with a smaller diameter (30–50 nm) performed better at high charge/discharge rates, owing to a higher number of primary particles per unit mass. This analysis aids in understanding material selection and its implications for battery design and lifecycle. The findings serve as a reference for future research exploring the use of CNTs in advanced battery materials.