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 ecological applications. Here, we propose a strategy for upcycling polyethylene terephthalate (PET) waste into polymer electrolytes through depolymerizing PET and then copolymerizing with oxalates, generating poly(terephthalate-oxalate) (PTO). PTOs show enhanced mechanical strength, primarily due to π–π interactions between the terephthalate units. 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 liquid : Li-salt molar ratio threshold of 1 : 1 is identified, beyond which the ionic conductivity significantly increases, but below which the ionic conductivity cannot be clearly increased. PTO-based QSSEs allow the long-term stable cycling of high-voltage Li//LiNi_0.85Mn_0.075Co_0.075O₂ cells. Furthermore, the 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 waste into high-value polymer electrolytes, establishing a closed-loop application for plastics.