Freeze-drying induced gradient microporous composite film with high ionic conductivity for ultrasensitive wearable iontronic pressure sensor

• Low temperature synthesis significantly increases the ionic conductivity of gel polymer . • Freeze-drying process produces gel polymer with a unique gradient microporous composite structure. • The iontronic pressure sensor demonstrates an extraordinary sensing performance. • The iontronic sensor enables high sensitivity monitoring of physiological information. Flexible pressure sensors are essential and key components for wearable electronics, but they have many limitations. The requests for a simple, fast, and low-cost fabrication method for ultrasensitive sensors hold practical significance. In this paper, we introduce an innovative ionic film with gradient porous structures and high ionic conductivity, synthesized using a facile casting and freeze-drying method, to fabricate flexible iontronic pressure sensors. We demonstrate that low synthesis temperatures markedly enhance hydrogen bond number of the ionic films, as revealed by Molecular Dynamics simulation, thereby significantly increasing the ionic conductivity of the film to an impressive value of 6.62 mS/cm, more than twice of the best values reported. The films exhibit a composite structure comprising layered pores and a rough surface. Leveraging these properties, this ionic film-based iontronic capacitive pressure sensor achieves an unprecedented sensitivity of 13786.2 kPa −1 and a broad pressure sensing range of 300 kPa, and is capable of distinguishing subtle pressures as low as 0.1 Pa, featuring a remarkably swift response time of 8 ms. We demonstrate that the sensor and its array could perform sensitive and accurate monitoring of physiological information and physical activities, and act as an excellent human–computer interface. This study offers an innovative and scalable approach to dramatically enhance sensor performance for various applications.