Molecularly engineered cellulose hydrogel electrolyte for highly stable zinc ion hybrid capacitors

Zinc ion hybrid capacitors (ZIHCs) are promising candidate for potential large-scale energy storage, but they still suffer from trade-off in energy density and cycling life originated from Zn dendrite growth and side reactions. Herein, we proposed a sustainable molecular engineering strategy of in situ derivatization of cellulose and composition by taking the particular cellulose solution properties in the superbase/DMSO/CO2 solvent system to prepare a carboxylic acid functionalized cellulose (COOH-f-Cell) hydrogel electrolyte capable of regulating Zn electro-deposition behavior. The findings indicated that the solubilization and derivatization of cellulose expanded the inherent inter-/intra hydrogen bonds network, resulting in the formation of unblocking ion channels with grafted carboxylic acid groups. Impressively, carboxylic acid functional groups achieved the homogeneity of the Zn electrodeposition process and induced the formation of a flat stacking layer of (002) crystal planes, thus effectively inhibiting Zn dendrites. Consequently, the cycle stability of the Zn plating/stripping in symmetrical Zn||Zn cell exceeded 5250 h at 0.5 mA cm-2 (over 7.3 months). The ZIHCs delivered a superb cycling life of 70,000 cycles with 91 % capacity retention at 5 A g-1. This strategy proposed here opens up a fresh route for using cellulose hydrogel electrolytes to regulate the deposition behavior of Zn2+ for high-performance zinc-based energy storage systems.