Imidazolium-functionalized Ionic Polyurethanes based Self-Healable Triboelectric Nanogenerator with Enhanced Performances

Triboelectric nanogenerator (TENG) is one of the promising energy harvesting technologies which converts ambient mechanical energy to electrical energy. In order to advance in next-generation soft electronic devices, the TENG is required to be flexible, stretchable, and biocompatible. In addition, the ability of autonomously self-healing after mechanical damage is highly desired for durability and stable production of electrical energy. Thermoplastic polyurethane (TPU), a multi-block copolymer composed of hard and soft segments, can control its electrical and mechanical properties through chemical modification. Also, TPU has advantages such as elasticity, flexibility, and mechanical strength. Therefore, a lot of research on self-healing polyurethane TENG based on disulfide bond, and borate bond has been reported so far. However, research on materials that can simultaneously increase output as well as self-healing is still needed. So, in this study, we synthesized imidazolium-based ionic polyurethane to fabricate high output performance and self-healable TENG. Imidazolium-based ionic polyurethane was intended to have biocompatible properties using polycaprolactone diol and hexamethylene diisocyanate. In addition, using imidazolium ionic liquids diol, an ionic polymer composed of a polymer backbone and an ionic liquid (IL) species was prepared for each repeating unit. As a result, the IL moieties consisting of loosely bound bulky cations and anions can form the electrostatic interaction to form self-healing TENGs. If there is a small scratch on the TENG, it will heal and return to its original state after about an hour. Even in an entirely cut state, it can be fully healed after 24 hours at a temperature of 50 degrees and has the same mechanical properties as before. IL not only affects self-healing, but also greatly affects TENG output performance. ILs could form the electrical double layer (EDL) by their high capacitance and mobile ions. So, we checked the output change while gradually increasing the proportion of imidazolium ionic liquids. As a result, it was confirmed that (1,1) has the highest output. In addition, we confirmed that when the molecular weight of PCL was lowered, and a fluorine unit was included under the (1,1) condition, the output was dramatically increased, resulting in a maximum 650 V and 47 μA output. Finally, the power density is 13.5 times greater than when imidazolium ionic liquids are not included, resulting in 1243 μW/cm² . So, this imidazolium-based ionic polyurethane TENG demonstrated a possibility of high output performance and self-healable TENG for electronic devices.