An overview of flexible sensors from ionic liquid-based gels

Ionic liquid (IL)-based gels (ionogels), which consist of ILs and polymer networks, are emerging materials with extraordinary properties, such as good ionic conductivity, outstanding transparency, tunable mechanical properties, and excellent stability in harsh environments. Based on these exceptional characteristics, ionogels show irreplaceable prospects in flexible sensors. In recent years, significant advancements have been made in designing flexible sensors based on ionogels. In this review, recent progress in various ionogel-based flexible sensors, including strain sensors, pressure sensors, temperature sensors, and other kind of sensors, is comprehensively overviewed. The material design, working mechanism, sensing performances, and applications for each kind of sensor are systematically elaborated. Subsequently, the commonly adopted methods to prepare ionogel-based sensors are introduced. The advantages and disadvantages of each method are discussed for guiding the design of desired ionogel-based flexible sensors. Finally, the open issues and challenges that currently impede practical applications of ionogel-based flexible sensors are thoroughly presented.