<p>Phase-change energy storage materials are of great significance for the efficient utilization of solar energy. However, conventional calcium carbonate-based phase-change microcapsules usually suffer from weak light absorption and relatively low photothermal conversion efficiency. In this study, an electrostatic self-assembly strategy was employed to load carboxylated carbon nanotubes onto the surface of calcium carbonate-based phase-change microcapsules through surface potential regulation, thereby constructing CNTs@CaCO₃-MEPCM composite microcapsules. The effect of CNTs loading on the photothermal energy-storage performance of the microcapsules was systematically investigated. The results show that, at a CNTs loading of 4 wt%, the composite microcapsules maintained a phase-change enthalpy of approximately 104&#xa0;J/g, while achieving a latent-heat-based photothermal storage efficiency of 88.46% and a thermal conductivity of 0.9267&#xa0;W·m^− 1·K^− 1. After 500 thermal cycles, the sample still retained stable phase-change behavior, indicating good thermal reliability. Compared with representative reported photothermally functionalized MEPCM systems, the present material exhibits a relatively balanced performance among photothermal energy storage, heat transfer, and latent-heat storage capabilities. This study provides a feasible strategy for designing composite phase-change microcapsules with integrated photothermal conversion and energy-storage capabilities, offering useful guidance for solar thermal utilization and building energy-efficiency applications.</p>