Influence of Cellulose Phthalation on the Supercapacitor Performance of a Cellulosic Gel Electrolyte

Cellulose-based gel polymer electrolytes show great potential for electrochemical supercapacitors due to the abundance, renewability, and structural versatility of cellulose. However, weak interactions between unmodified cellulose and organic electrolytes usually lead to low ionic conductivity, limited specific capacitance, and unsatisfactory cycling stability. Dissolving pulp─a variety of cellulose pulp with high purity and reactivity─can be easily chemically modified to improve conductivity. In this context, cellulose phthalate (CP) was synthesized from bamboo dissolving pulp via esterification in dimethylacetamide/lithium chloride. The modified dissolving pulp was then employed as a gelator to fabricate organic gel electrolytes with dimethylformamide/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The influence of the degree of substitution of CP on the supercapacitor performance of the gel electrolyte is studied. Taking advantage of the enhanced coordination of the TFSI – sulfoxide with cellulosic phthalate groups, the optimized gel electrolyte exhibits high ionic conductivity and stable electrochemical behavior. A specific capacitance of 88 F·g –1 and excellent cycling stability (99.5% retention after 5000 cycles at 1 A·g –1 ) are achieved using simple activated carbon electrodes in a symmetric supercapacitor. Overall, the phthalation method has the potential to endow dissolving pulp feedstock with attractive high-value functionality that can make it useful for supercapacitors and other applications.