Architecting Highly Anisotropic Thermal Conductivity in Flexible Phase Change Materials for Directed Thermal Management of Cylindrical Li-Ion Batteries.

The anisotropic jelly roll structure of cylindrical Li-ion batteries leads to highly directional heat generation, causing severe radial heat accumulation and creating a critical demand for precise thermal management. Conventional anisotropic phase change materials (PCMs), often reliant on single-dimensional conductive skeletons, exhibit limited enhancement in thermal conductivity anisotropy. This study proposes a novel strategy utilizing a hybrid carbon aerogel composed of one-dimensional carbon nanotubes (CNTs) and three-dimensional expanded graphite (EG) to construct highly aligned thermal conduction pathways within a flexible PCM. A three-step experimental method was employed to successfully fabricate a composite PCM with highly anisotropic thermal conductivity. A case study confirmed that, compared to a sole 3D skeleton, the hybrid 1D/3D aerogel significantly improves the alignment of the microstructure. At an optimal hybrid aerogel content of 8 wt.%, the composite achieved a 5.0% increase in radial thermal conductivity and a remarkable 16.7% increase in axial thermal conductivity, indicating a significantly optimized anisotropy ratio. When applied to a cylindrical battery thermal-management case, this material enables directed heat dissipation, effectively lowering the maximum battery-surface temperature by 13.1 °C. This work provides a scalable approach for designing high-performance anisotropic flexible PCMs tailored for advanced thermal management in high-power-density Li-ion batteries and other compact electronics.