Ultra-sensitive, lightweight, and flexible composite sponges for stress sensors based combining of "through-hole" polyimide sponge and "pleated stacked" reduced graphene oxide

For the advantages of light weight, rapid recovery, and high sensitivity, the conductive flexible composite sponges with idiographic spatial structure as a stress sensor has received great attention. However, for small pressure and deformation, it is still challenging to achieve high sensitivity and response. Here, the polyimide (PI) sponge with through-hole structure and special functional groups is successfully fabricated through a clever structural design and is used as substrate of the composite sponges. The new PI sponge effectively induces the fabrication of reduced graphene oxide (RGO) sponge that possessing a pleated stacked structure in the cells only by a hydrothermal route. By controlling the GO dispersion concentration, the maximum electrical conductivity of the composite sponges reaches to 10.68 x 10-4 S/m. The maximum sensitivity of composite sponges arrives at 1.172 kPa-1 and possesses a wide response range from 0 to 1 kPa. Comparing with previous similar works, the maximum sensitivity is improved by 74.9-1231.8%. Meanwhile, composite sponges exhibit excellent cycling stability under different compression rates, and present obvious response to tiny stress or deformation which is as low as 0.09 N and 0.45%. This is of great significance for the application of the conductive composite sponges sensor in tiny stress.