<p>In vertical latent heat thermal energy storage (LHTES) systems, natural convection tends to induce temperature gradients and uneven liquid-phase distribution during phase transition, thereby limiting overall thermal performance. To enhance heat transfer uniformity, this study proposes a novel lid-shaped fin structure. Based on the validation of the numerical model, a systematic comparative analysis is conducted between the proposed structure and conventional annular fins regarding their thermal behaviors during both melting and solidification processes. Furthermore, the influence of fin orientation on transient heat transfer performance is investigated. Key evaluation metrics include the evolution of liquid fraction, spatial distribution of liquid-phase phase change material (PCM) and temperature fields, as well as uniformity indices for liquid fraction and temperature. The results indicate that the lid-inspired fins significantly enhance thermal performance during both charging and discharging processes, with particularly notable improvements observed during charging. The proposed fin design effectively optimizes the temperature field distribution, alleviates heat transfer lag regions, and substantially reduces the time required for both melting and solidification. Among the various orientation schemes tested, the downward-facing lid configuration exhibits the best thermal performance. Compared to conventional annular fins, the complete melting time, solidification time, and total time are reduced by 29.95%, 12.45%, and 22.63%, respectively. These findings provide valuable theoretical insights and practical guidance for the structural optimization of fin configurations in PCM-based thermal energy storage systems.</p>