Lignin-Based Gel Polymer Electrolyte for Cationic Conductivity

The article presents the results of the preparation and study of a gel-polymer electrolyte based on lignin obtained from Pinus sylvestris. Sulfonation and subsequent chlorination of lignin make possible implementation of the principle of mono-ionic conductivity in a natural biopolymer matrix, which provides predominantly cationic conductivity of the electrolyte. Based on the results of the qualitative and quantitative analysis of the synthesized samples, the mechanisms of the chemical conversion of the biopolymer, the structure models of the converted fragments of macromolecules, as well as the quantum-chemical calculation of their electronic and geometric parameters are presented. The key electronic characteristics of the gel polymer electrolytes (GPE) based on a composite of lignins with 20 wt.% polyvinyl alcohol are determined by impedance spectroscopy. The maximum value of the specific volume conductivity is 2.48 × 10^-4 S cm^-1, which is comparable with most commercial electrolytes of this type, but at the same time, record values are reached in the number of lithium cation transfer tLi+ of 0.89. The studies allow to identify the basic laws of the effect of chemical modification on the structure of GPE and describe the mechanism of ionic conductivity.