Flexible and Thermally\nStable ATRP-Modified Lignin/PEO\nComposite Membrane

To utilize lignin, which is a sustainable natural polymer,\na star-like\nlignin-<i>graft</i>-polyethylene glycol methacrylate–glycidyl\nmethacrylate (LGPG) polymer was prepared via solvent extraction and\natom transfer radical polymerization (ATRP). Ethyl acetate-extracted\nlignin, obtained from the solvent extraction of Kraft lignin (KL),\nexhibited higher reactivity in ATRP, resulting in the synthesis of\na star-like structure with a higher degree of polymerization than\nKL. The resulting LGPG/poly(ethylene oxide) (PEO) composite membranes\nexhibited high thermal stability and excellent elongation at break\nof 598.56% (with 0.3 g of LGPG). These findings indicated that LGPG\nimparted more flexible properties to the membranes than those made\nsolely of PEO. Moreover, the addition of LGPG to the composite membrane\ndecreased the glass transition temperature and crystallinity. These\nresults indicated a plasticizing effect due to the high free volume\nand flexible multiarm structure of the star-like polymer, which disrupted\nthe PEO chain packing within the membrane. This plasticizing effect\nresulted in LGPG/PEO composite membranes with high ionic conductivity\nwhen used as solid polymer electrolytes (SPEs). Furthermore, the performance\nof coin cells using LGPG/PEO composite membranes in lithium–lithium\nsymmetric cell lithium plating/stripping tests revealed a lower and\nmore stable voltage profile than that of the PEO membrane following\n50 charge/discharge cycles. This study highlights the potential of\nATRP as a favorable method for synthesizing SPEs using lignin in electrochemical\napplications.