Ultralight, flexible, and thermally insulating mullite nanofiber aerogels for extreme temperature applications and battery safety

Ceramic aerogels have attracted significant attention due to their ultralight weight, high porosity, and multifunctional properties. However, achieving mechanical robustness, thermal shielding capability, and simple fabrication simultaneously under extreme environments remains challenging. Herein, an electrospinning strategy based on the combined hydrolysis of dual aluminum sources (AlCl₃·6H₂O and aluminum isopropoxide) is proposed. Except for the conventional polymer spinning aid used to improve spinnability, no additional acid/base regulators are introduced. By regulating the concentration of tetraethyl orthosilicate (TEOS) to optimize the entanglement of the nanofibers, mullite nanofiber aerogels (MFAs) with a three-dimensional “vine-like interlocking” fiber network are successfully fabricated. The obtained material exhibits a bulk density of 8–15 mg·cm⁻³ and a porosity of 99.44%, a room-temperature thermal conductivity of only 0.0315 W·m⁻¹·K⁻¹, and a transverse tensile stress of 813 kPa. They retain flexibility from −196 °C to 1500 °C, withstands 85% compressive deformation and 1000 compression cycles, and maintain structural integrity after high-temperature exposure, while also showing excellent acid and alkali corrosion resistance. A 1-cm-thick MFAs layer provides 25 s palm protection under a butane torch (1300 °C) and stabilizes the back-side temperature at 267.7 °C after 20 min. Moreover, a 3-mm-thick MFA layer effectively delays battery thermal runaway propagation. This study provides a new design strategy for highly stable and easily fabricated thermal management materials for extreme environments.