Multifunctional and Flexible 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 in applications such as buildings, wearable devices, and lithium-ion batteries (LIBs). However, conventional PCMs suffer from mechanical rigidity, leakage, and low thermal conductivity. In this study, multifunctional, flexible, and leakage-proof phase change composites (PCCs) are developed to overcome these limitations and enable dual-mode thermal regulation for all-climate LIBs. The PCCs provide Joule heating (22.5 °C min^-1) under subzero conditions to prevent lithium plating and restore capacity. Simultaneously, they deliver passive cooling to optimise the operating temperature of LIBs, acrosspower output scenarios (2C and 3C). The performance is further supported and validated through COMSOL simulations, which shed light on PCCs' phase change behaviour, the working temperature, and the heat distribution of LIBs. The integration of carbon nanofillers significantly enhances thermal conductivity by 240% while maintaining structural integrity. Additionally, the PCCs can function as overheating switches and temperature sensors (7.2%/°C at 40-45 °C) through a positive temperature coefficient (PTC) effect. Featuring low thickness (≈550 µm), leakage proof, and mechanical flexibility, these PCCs present a promising solution for advanced thermal management for safer and more efficient LIB operation.