Implantable CB/PVDF/TPU Sensors for In Situ Monitoring of Internal Temperature Changes in Lithium‐Ion Batteries

In situ monitoring of lithium‐ion battery thermal runaway is limited by the invasiveness and insufficient sensitivity of conventional thermometry. There is an urgent demand for non‐destructive, highly responsive, and stable sensing paradigms. Herein, we report an embeddable temperature sensor based on a 37 µm‐thick ternary composite film of carbon black (CB), poly(vinylidene fluoride) (PVDF), and thermoplastic polyurethane (TPU). By tailoring the CB mass fraction, constructing a dynamic TPU cross‐link network, and adopting an ultra‐thin architecture, the film simultaneously maximizes thermal responsivity and electrochemical compatibility. Interfacial nucleation induced by CB nanospheres increases the β‐phase content of PVDF, evidenced by fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) Battery Management System. The sensor achieves a response value of 0.7 under a 10°C temperature difference and maintains stable performance over 10 cycles. Integrated into a battery, it shows a resistance response of 0.56 for a 10°C change without affecting normal charge‐discharge cycles, and only a 16.7% increase in charge transfer resistance after 50 cycles, with capacity decay similar to the control group. By incorporating graph neural networks (GNNs), this study enables accurate internal temperature recognition and develops an early warning model for thermal runaway. The model achieves over 92% classification accuracy (AUC > 0.95) between 10°C and 40°C, supporting the development of high‐safety, intelligent battery management systems.