Structural modification of alkali lignin into higher performance energy storage materials： Demethylation and cleavage of aryl ether bonds

Lignin is extensively studied to be used as an energy storage material due to its intrinsic catechin structure. However, the limited content of catechin groups in industrial lignin is not enough to satisfy the demand for highly charged storage devices. Herein, the pseudocapacitance of lignin itself is further improved by demethylation and cleavage of aryl ether bonds of alkali lignin (AL) using the HBr/LiBr system. The phenolic hydroxyl (Ar-OH) group content of the demethylation alkali lignin (DAL, up to 2.99 mmol∙L−1) is 1.85 times higher than that of AL. The as-prepared DAL@ reduced graphene oxide (rGO) composites obtained from DAL and graphene oxide (GO) showed excellent energy storage capacity (414.5 F∙g−1), which increased by 96.60% compared to the AL@rGO composites. More significantly, the DAL@rGO materials displayed excellent rate capacity, and its capacitance retention rate reached 76.91%. Therefore, this strategy of structural modification of lignin is effective for improving its energy storage performance, which will provide a possibility for the development of lignin into higher-performance energy storage materials. [Display omitted] •Lignin modification constructs more catechol structures to improve its pseudocapacitance.•The treated lignin Ar-OH content is 1.85 times higher than alkali lignin.•96.6 % improvement in specific capacitance of supercapacitors.