Composite Material Based on N‐Tetradecanol and Expanded Graphite for High‐Efficient Thermal Storage

To overcome low thermal conductivity and leakage in organic phase change materials (PCMs), a high‐performance composite is developed by combining n‐tetradecanol (TD, 92.3 wt%) with expanded graphite (EG) via vacuum impregnation. Pure TD exhibits high latent heat (243.82 J g −1 melting, 246.48 J g −1 solidification) but suffers from leakage and low conductivity (0.355 W m −1 K −1 ). Leveraging EG's porous structure (33.16 m 2 g −1 Brunauer–Emmett–Teller) and high conductivity (8.161 W m −1 K −1 ), the optimized TD/EG composite (12:1 ratio) achieves latent heats of 218.84 J g −1 (melting) and 216.80 J g −1 (solidification), retaining ≈90.0% of TD's capacity, with stable phase transition temperatures (≈35.6‐35.7 °C). Crucially, thermal conductivity reaches 7.353 W m −1 K −1 (20.7x improvement), leakage is eliminated (≤1.1% mass loss), and chemical stability is confirmed (Fourier‐transform infrared [FTIR]/X‐ray diffraction). After 1,200 thermal cycles, 94.7% latent heat is retained (207.17/204.16 J g −1 ) with minimal temperature drift (<0.85 °C). This resolves the trade‐off between energy density, thermal response, and reliability, establishing the composite as a benchmark for leak‐free, high‐conductivity thermal energy storage in solar and electronics applications.