Fully Biobased\nHigh-Strength and High-Toughness Double\nCross-Linked Cellulose Hydrogel for Flexible Electrolytes

A simple and feasible method to prepare fully biobased\nhydrogels\nwith high mechanical strength and toughness remains a great challenge.\nHerein, different types of biobased long-chain chemical cross-linking\nagents, epoxy vegetable oils, were used in combination with a double\ncross-linking strategy to prepare fully biobased cellulose hydrogels,\nand their feasibility as electrolyte materials for flexible energy\nstorage devices was investigated. Through continuous chemical and\nphysical cross-linking, these hydrogels achieved high water contents\n(60–80%) and excellent mechanical properties (under the same\nconditions, the maximum strain can reach 290% under tension and the\ntoughness was 9.8 MJ m<sup>–3</sup> and the maximum strain\nwas 58% and 0.6 MJ m<sup>–3</sup> under compression). At the\nsame time, due to the inherent hydrophobicity of vegetable oil, the\nhydrophobic stacking of cellulose chains was increased, thereby promoting\nself-assembly and recrystallization in the subsequent cross-linking\nprocess, resulting in a unique nanoporous structure of the internal\ncross-linked network. After being fully immersed in the electrolyte,\nthe ionic conductivity at room temperature was as high as 35.4 mS\ncm<sup>–1</sup>. In addition, the assembled corresponding flexible\nzinc-ion hybrid capacitor showed the ability to power wearable electronic\ndevices. Hence, this study provides a new approach for the construction\nof strong and tough fully biobased hydrogels and their applications\nin the field of flexible or wearable electronic devices.