Direct-Printed Mn–Ni–Cu–O/Poly(vinyl butyral) Composites for Sintering-Free, Flexible Thermistors with High Sensitivity

Manganese-based spinel ceramic materials represent a class of typical negative temperature coefficient thermistors, which have found extensive applications in the aerospace, marine, and automotive industries. However, with the growing demand for flexible, lightweight, and miniaturized electronic devices, conventional ceramic-based temperature sensors─fabricated via high-temperature sintering and limited by intrinsic rigidity and poor processability─are progressively failing to meet the temperature sensing and control requirements of next-generation electronics. Furthermore, most existing flexible temperature sensors rely on carbon-based nanomaterials, conductive polymers, or metallic materials as sensing elements, which often exhibit limited sensitivity and narrow operational temperature ranges, thereby considerably constraining their practical utility. In this work, an organic–inorganic composite strategy was employed to develop a temperature-sensitive material that integrates the high sensitivity of metal oxides with the flexibility of polymers, processable at a low temperature of only 200 °C. By incorporating polyvinyl butyral (PVB) into Mn–Ni–Cu–O (MNCO) ink, the stability of the ink and the functional properties of the composite were effectively modulated. The MNCO/PVB composite fabricated by direct printing demonstrates a broad operating temperature range from −60 to 100 °C, a high sensitivity of −8.35%/°C, and a rapid response time of 1.79 s. The directly printed MNCO/PVB thermistor enables continuous, stable, reproducible, and rapid temperature monitoring. It is noteworthy that the low processing temperature of 200 °C ensures high compatibility with most flexible substrate technologies. This highly sensitive and flexible thermistor, processed at low temperatures, offers a viable strategy for the development of wearable devices suitable for health monitoring and exercise guidance.