Cellulose ionogels: Recent advancement in material, design, performance and applications

• Cellulose-based ionogels are essential for developing flexible electronics • Cellulose types, gel mechanism, and applications of inongels are presented • Suggesting directions focus on performance enhancement and application expansion Due to the features and wide range of potential applications, cellulose ionogels are the subject of extensive research. Green celluloses have been employed as a three-dimensional skeleton network to restrict the ionic liquids (ILs) toward advanced ion-conductive ionogels. Diversiform cellulose ionogels with desirable performances, via physical/chemical reactions between cellulose and ILs, have been harvested, which have the potential to emerge as a bright star in the field of flexible electronics, such as sensors, electrolyte materials as power sources, and thermoelectric devices. Herein, a review regarding cellulose ionogels in terms of fundamental types of cellulose, formation strategies and mechanism, and principal properties is presented. Next, the diverse application prospects of cellulose ionogels in flexible electronics have been summarized. More importantly, the future challenges and advancing directions to be explored for cellulose ionogels are discussed. Cellulose serves as the solid matrix to constrain the flowing ILs in the ionogel system by crosslinking with physical or chemical means, which not only solves the problem of leakage caused by the fluidity of ILs but also inherits the excellent physical and chemical properties of ILs and the high mechanical strength of the solid matrix. The intrinsic multi-scale cellulose and unique ILs derive diversified functional properties and applications. Cellulose ionogels has appeared as a promising candidate for flexible electronics. In this section, many applications of cellulose ionogels will be investigated, like sensor, supercapacitor, lithium-ion batteries, dye-sensitized solar cell, and thermoelectric device.