Upgraded Closed-loop Recycling of PET for High-voltage Solid-state Electrolytes and Their Critical Li+ Transport

Abstract

Advancing clean energy and waste recycling is essential for green ecology. Here, we propose a strategy of upcycling polyethylene terephthalate (PET) wastes into polymer electrolytes through depolymerizing PET and then copolymerizing with oxalates, generating poly(terephthalate-oxalate) (PTO). Contributed from the π-π interaction between terephthalate units, PTOs show enhanced mechanical strength. We examine the Li+ migration mechanism in quasi-solid-state electrolytes (QSSEs), which is determined by the polymer-solvent affinity and the solvation degree of Li+-migration-intermediates. A threshold of liquid:Li-salt molar ratio is identified at 1:1, beyond which, the ionic conductivity significantly increases, but below which, the ionic conductivity cannot be raised obviously. The PTO-based QSSEs allow the long-term stable cycling of high-voltage Li//LiNi0.85Mn0.075Co0.075O2 cells. Furthermore, this PTO can be recovered from the spent QSSEs through high-efficiency alkaline hydrolysis. This study reveals the Li+-migration mechanism in QSSEs and demonstrates the chemical upcycling of PET wastes into high-value polymer electrolytes, establishing a closed-loop application of plastics.