Series-structured design for enhanced pyroresistive properties in low switching temperature PTC composites

Positive temperature coefficient (PTC) composites with low switching temperature (T s ) are critical for self-regulating heating in spacecraft optical systems and energy systems, nevertheless, balancing low initial resistivity, high PTC intensity, and fast heating rate is still challenged. This work designs a novel low T s PTC composite with series structure to conquer such contradictions, comprising a PTC switching module as interlayer and highly conductive heating modules as upper/lower layers. The architecture simultaneously leverages the sharp PTC effect of interlayers and rapid heating effect of upper/lower layers, resulting in obvious advantages in pyroresistivity properties and self-regulating heating performance. The series-structured composite achieves improved PTC intensity of 6.7 with the corresponding heater average heating rate of 25.8 °C/min, in comparison to 6.2 and 7.8 °C/min for the conventional PTC composite, while these two composites possess similar low T s (38 °C) and initial resistivity (45 Ω cm). The series-structured composite also demonstrates exceptional reproducibility of pyroresistivity properties with 89 % resistivity retention over 500 heating-cooling cycles. Furthermore, as an innovative design architecture transcending compositional constraints, adjusting module compositions enables flexible tuning of pyroresistivity properties of the series-structured composites and average heating rates and equilibrium temperatures of the corresponding heater without compromising stability. This work provides a new guideline for developing low T s PTC composites with potential applications in customizable aerospace de-icing, automotive heaters, and battery thermal management systems.