Thermal Anisotropy Ratio >1000 in Solution-Spun Macroscopic Carbon Nanotube Films

Films with large anisotropy ratios (r) between the in-plane and cross-plane thermal conductivity (κ) can be used for directional heat spreading in electronics thermal management. Here, we show that commercially available solution-spun carbon nanotube (CNT) films with 20 μm thickness and centimeter-scale lateral dimensions exhibit orthotropic thermal conductivity with the highest reported r to date, reaching r = 1400 ± 160 at room temperature (T). We find r using laser flash thermal diffusivity (α) measurements over a T range from 198 to 573 K. Dedoping of acid residuals via annealing increases the in-plane-aligned α_x of dedoped samples by a factor of 2 compared to the doped samples. These dedoped CNT films also display a strong α_x ∝ T^-1.1 scaling, indicating that phonon-phonon scattering impacts heat transport along the direction of alignment. Our work motivates further exploration of ultrahigh r in macroscopic CNT materials and applications of CNT films for directional heat spreading.