Gel-Electrolyte-Coated Carbon Nanotube Yarns for Self-Powered and Knittable Piezoionic Sensors

Piezoionic materials are potential smart soft materials because of their similarity to biological systems in signal generation and transmission but still have limited use due to their intrinsic low response strain, noisy signal output, and complex structure. We report herein that the piezoelectric effect can be observed on an electrolyte-coated high-surface-area carbon nanotube yarn, generating large lengthwise voltage gradients without the assistance of an external electrical bias when the yarn was stretched. A mechanism of dynamic structure-nonuniform-induced ion squeezing is proposed to explain the electricity generation along the conductive piezoionic yarn. Between the two ends of the yarn, sensitive and high-recognition voltage signals with ultralow noise are generated, when the yarn is subjected to mechanical stretching at a wide range of strains and frequencies. The voltage polarity is tuned by selecting a proper type of absorbed ions. Knitting of the piezoionic yarns as a self-powered sensor into a glove is demonstrated for precisely recognizing hand gestures and human-machine interactions. Because of features such as a simple structure, easy fabrication, high flexibility and stretchability, and a wide range of response, this piezoionic yarn is promising for smart textiles, wearable sensing devices, and implantable artificial muscle feedbacks.