Negative Poisson's Ratio in Cellulose Nanocrystal Aerogels for Enhanced Sports Piezoelectric Sensing

Cellulose nanocrystal (CNC)-based aerogels hold promise as materials for piezoelectric sensors, given their biodegradability, cost-effectiveness, and adaptable mechanical properties. However, cellulose-based mechanoelectrical sensors often suffer from limited performance due to poor sensitivity and output, arising from inadequate stress transfer and mechanoelectrical coupling. In this study, a novel metastructure with a negative Poisson's ratio (NPR) is introduced to boost the piezoelectric performance of cellulose-based aerogel sensors. To activate crystal-based piezoelectricity and maintain the aerogel's flexibility, CNC crosslinked with flexible polyethylene glycol (PEG) is utilized. A biaxial compression method is employed to create anisotropic NPR structures, which achieve self-polarization of this piezoelectric device. The results show that the NPR structure, which presents asymmetric auxetic properties, amplifies the piezoelectric output voltage by 25.7-fold. Moreover, the piezoelectric output voltage density and the d 33 $d_{33}$ piezoelectric constant reach impressive values of 1.64 × 10 6 $1.64\times 10^6$ V · ${\rm V}\cdot$ m − 3 ${\rm m}^{-3}$ and 5.33 pC N − 1 ${\rm N}^{-1}$ , respectively. The NPR aerogel-based piezoelectric device, with a series-parallel connection, exhibits high output stability and has potential applications in monitoring various human sports activities.