A Robust Dual‐mode Self‐Monitoring Battery Thermal Management System via Bilayer Structural Design

Battery thermal management (BTM) materials based on water evaporation have shown great potential for ensuring safe and efficient operation of batteries because of acceptable cooling efficiency and low cost. However, it remains a great challenge to realize their practical applications due to unsatisfactory cooling efficiency, and lack of preheating and self‐monitoring capability. Herein, this study proposes a bilayer structural design strategy to develop a robust dual‐mode (cooling and preheating) and hydration‐level self‐monitoring BTM material by integrating a hygroscopic bilayer of adhesive hydrogel/carbon fiber felt (AH/HCFF). The tough thermally conductive hydrogel enables robust interfacial contact with battery, leading to a low interfacial thermal resistance, and the carbon fiber felt with high thermal conductivity ensures a high through‐plane thermal conductivity. The AH/HCFF achieves a cooling efficiency of 53.9%, surpassing existing counterparts. Because of broadband light absorption, the AH/HCFF exhibits a strong photothermal conversion capacity in the UV‐vis‐NIR range, enabling it to repeatedly preheat batteries in low‐temperature conditions. Also, it shows an excellent moisture‐electric generation capability, achieving a maximum output power density of 38.6 µW cm −2 , thus making it real‐time monitor its cooling performance and working status. This work provides a promising solution to developing adaptive intelligent BTM systems and expedites their real‐world applications.