Multifunctional, flexible, and biodegradable phase change composites for Dual-mode thermal management of lithium-ion batteries

Phase change materials (PCMs) are highly renowned for their substantial latent heat capacity, enabling efficient thermal management for electronic devices. However, conventional PCMs face significant limitations, including mechanical rigidity, leakage, and low thermal conductivity. In this study, we developed multifunctional, flexible, and leakage-free phase change composites (PCCs) using biodegradable materials. The proposed PCCs exhibit dual-mode thermal management capabilities: they provide Joule heating (22.5°C/min) under subzero conditions to prevent lithium plating and recover capacity, while also delivering passive cooling to optimise the operating temperature of lithium-ion batteries (LIBs) across diverse power output scenarios. The practical performances are further supported and validated through COMSOL simulations, illustrating the phase change behaviour of PCCs, working temperature, and heat distribution of LIBs. The integration of carbon nanofillers substantially enhances the electrical (10 S m^-1) and thermal conductivity (0.72W/mK) of the composites. Additionally, the PCCs function as temperature sensors (7.2*10³ppm/°C) and safety switches, issuing hazard alerts when LIBs operate within risky temperature ranges and acting as over-current switches to prevent overheating through a positive temperature coefficient (PTC) effect. With a low thickness (~550 µm), mechanical flexibility, and biodegradable composition, these PCCs present a promising solution for advanced thermal management in energy storage systems, offering safer and more efficient LIB operation. Furthermore, these properties make them well-suited for integration into emerging sectors such as flexible electronics and wearable technologies, where both thermal management and mechanical adaptability are crucial.