The development of efficient thermal energy storage (TES) materials is vital for improving energy utilization and supporting renewable and industrial heat recovery systems. However, conventional molten-salt phase change materials (PCMs) often exhibit low thermal conductivity and poor interfacial wettability, which limit heat-transfer efficiency and storage performance. This study investigates the effect of multi-walled carbon nanotube (MWCNT) doping on the thermophysical and interfacial properties of lithium-based eutectic salts with different compositions—binary (LiK), ternary (LiT), and quaternary (LiQ). The results show that low MWCNT concentrations (0.1–0.3 wt.%) enhanced latent heat by up to 8 % and thermal conductivity by 12–15 %, whereas specific heat showed modest improvement. Contact angle analysis indicated a significant decrease in surface angle, confirming improved wettability and stronger interfacial heat transfer. Scanning electron microscopy images revealed uniform nanoparticle dispersion and compositional stability, confirming the chemical compatibility of the nanocomposite salts. These findings demonstrate that optimized MWCNT incorporation can simultaneously enhance both thermophysical and interfacial properties of lithium-based eutectic salts. The study provides comparative and mechanistic insights into the role of nanocarbon doping in improving the performance of molten-salt PCMs, offering a pathway for the design of advanced TES materials with improved efficiency and stability. The novelty of this study lies in its comparative evaluation of MWCNT-doped lithium-based binary, ternary, and quaternary eutectic salts under identical conditions, and in correlating interfacial wettability with thermophysical enhancements. This integrated approach establishes a mechanistic understanding of how carbon nanostructures modify molten-salt behavior. The findings provide a scientific framework for designing next-generation PCMs with improved efficiency and reliability for high-temperature TES applications.