A cradle-to-cradle approach for successive upcycling of polyethylene to polymer electrolytes to organic acids

Abstract

Polymer electrolytes are poised to increasingly dominate energy storage devices such as lithium ion batteries (LiBs) in the near future. Although this has spurred development of new generations of polymer electrolytes derived from alternative non-petroleum feedstock by valorising societal waste, the solid electrolyte materials' end-of-life has thus far been largely overlooked. Inadvertently, their disposal contributes to the growing environmental and plastic waste pollution. To address this, we demonstrate herein a cradle-to-cradle upcycling approach for polymer electrolytes derived from polyethylene – the most abundant waste plastic produced annually. Polyethylene was first aerobically activated using N-hydroxyphthalimide organocatalysts, and subsequently modified to yield polyethylene-graft-polyester copolymers. Both components of the copolymers played synergistic roles to enable them to perform well as solid and gel polymer electrolytes with appreciable ionic conductivities. A prototype LiB cell formulated using the PE-derived copolymer as the gel polymer electrolyte showed high coulombic efficiency and excellent retention of charge/discharge capacity. Notably, we demonstrated the ease of chemically upcycling these post-use PE-polyester polymer electrolytes through organocatalytic oxidation to yield industrially relevant, short-chain dicarboxylic acids. Our method is tolerant to common additives such as lithium salts, even in significant quantities, thus enabling the polymer electrolytes to be directly upcycled without any additional pretreatment. Our approach of upcycling waste plastics into functional polymer electrolyte materials, which are in turn feedstock for further value creation at the end of their lives, provides a viable value chain for sustainable polymer electrolyte materials which can also be applicable to other functional materials derived from waste plastics.