Hierarchical Iontronic Flexible Sensor with High Sensitivity over Ultrabroad Range Enabled by Equilibration of Microstructural Compressibility and Stability

Despite improved sensitivity of iontronic pressure sensors with microstructures, structural compressibility and stability issues hinder achieving exceptional sensitivity across a wide pressure range. Herein, the interplay between ion concentration, mechanical properties, structural geometry, and aspect ratio (AR) on the sensitivity of lithium bis(trifluoromethanesulfonyl) imide/thermoplastic polyurethane (LiTFSI/TPU) ionogel is delved into. The results indicate that cones exhibit superior compressibility compared to pyramids and hemispheres, manifesting in an enhanced sensitivity toward the LiTFSI/TPU ionogel. Subsequently, by strategically combining cones with varying ARs, a harmonious balance between structural stability and compressibility is achieved, culminating in the fabrication of hierarchical iontronic flexible sensors (HIFS). Remarkably, HIFS-III with a three-level hierarchical conical microstructure demonstrates a preeminent sensitivity of 127.65 kPa^-1 within ∼500 kPa. Even within the ultrabroad pressure range of 1500-3000 kPa, the sensitivity remains exceeding 10 kPa^-1. Furthermore, HIFS-III boasts swift response and relaxation times (∼11 and 18 ms, respectively), a low detection limit (∼6.35 Pa), as well as remarkable durability (15,000 cycles). The exceptional sensing capabilities of HIFS-III underscore its emergence as a promising high-performance sensing and feedback solution tailored for applications in human-machine interaction and e-skin.