Aramid Nanofiber‐Based Janus Phase Change Composites Toward Multi‐Mode Adaptive Battery Thermal Management

ABSTRACT Phase change materials (PCMs) have garnered widespread interest in battery thermal management (BTM) for their excellent temperature regulation, high thermal storage density, and passive cooling without additional power consumption. Nevertheless, conventional PCMs fail to simultaneously mitigate capacity degradation caused by extremely high/low ambient temperatures and suppress battery thermal runaway (BTR) risks. Herein, a Janus‐structured phase change composite built on aramid nanofiber (ANF) aerogels, is engineered for multi‐mode adaptive BTM applications. The bilayer asymmetric architecture is constructed with boron nitride nanosheets embedded in the large‐pore ANF layer to deliver high thermal conductivity (1.860 W m −1 K −1 ) and large latent heat (189.23 J g −1 ) after PCM impregnation, while fluorosilane modification imparts the small‐pore ANF layer remarkable thermal insulation (0.028 W m −1 K −1 ) and flame retardancy. The as‐resulted composite with a thickness of 7 mm achieves an 8.60°C reduction in the surface temperature for commercial 2000 mAh lithium‐ion batteries under 3 C charge/discharge cycling. It also drastically decreases the peak runaway temperature from 798.29°C to 240.85°C and effectively blocks BTR propagation between adjacent cells. Meanwhile, the composite raises the usable discharge capacity from 770 to 1275 mAh at −20°C, offering a promising strategy for developing multi‐mode adaptive BTM systems.