Fully Biobased High-Strength and High-Toughness Double Cross-Linked Cellulose Hydrogel for Flexible Electrolytes

A simple and feasible method to prepare fully biobased hydrogels with high mechanical strength and toughness remains a great challenge. Herein, different types of biobased long-chain chemical cross-linking agents, epoxy vegetable oils, were used in combination with a double cross-linking strategy to prepare fully biobased cellulose hydrogels, and their feasibility as electrolyte materials for flexible energy storage devices was investigated. Through continuous chemical and physical cross-linking, these hydrogels achieved high water contents (60–80%) and excellent mechanical properties (under the same conditions, the maximum strain can reach 290% under tension and the toughness was 9.8 MJ m–3 and the maximum strain was 58% and 0.6 MJ m–3 under compression). At the same time, due to the inherent hydrophobicity of vegetable oil, the hydrophobic stacking of cellulose chains was increased, thereby promoting self-assembly and recrystallization in the subsequent cross-linking process, resulting in a unique nanoporous structure of the internal cross-linked network. After being fully immersed in the electrolyte, the ionic conductivity at room temperature was as high as 35.4 mS cm–1. In addition, the assembled corresponding flexible zinc-ion hybrid capacitor showed the ability to power wearable electronic devices. Hence, this study provides a new approach for the construction of strong and tough fully biobased hydrogels and their applications in the field of flexible or wearable electronic devices.