Ion gradient induced self-powered flexible strain sensor

To cope with energy hazards and reduce frequent battery replacement of strain sensors, various self-powered flexible strain sensors (including piezoelectric, triboelectric and electrochemical types) have developed recent years. However, the piezoelectric and triboelectric strain sensors cannot monitor static strain, and electrochemical strain sensors face the problem of performance degradation. Herein, inspired by ion gradient generators, a self-powered flexible strain sensor based on strain regulated ion gradient strategy is constructed. The sensor consists of elastic yarn coated with carbon nanotubes (CNTs), LiCl-filter paper (FP) and latex tube encapsulation. LiCl-FP with excellent water molecules absorption performance is wrapped on one side of the elastic yarn, forming a high humidity region in the sensor. The part of the elastic yarn that is not covered by LiCl-FP has weak water molecules absorption performance, forming a low humidity region in the sensor. The ions in the sensor move directionally from the high humidity region to the low humidity region, forming an ion gradient and generating voltage/current. The test results indicate that the sensor exhibits a wide strain detection range (0.5%–100%) and good repeatability (1000 times). The strain sensing mechanism can be attributed to the strain regulated ion gradient and the resistance strain effect. In addition, the strain sensing function of the sensor is verified by monitoring respiration. This work opens a new avenue for development of self-powered strain sensor using strain regulated ion gradient.