Fully Recyclable, Catalyst-Free, Highly Adhesive, and Resilient Poly(β-Amino Esters) Covalent Adaptable Network-Based Solid Polymer Electrolytes for Lithium Metal Batteries

Abstract

Despite the widespread adoption of lithium-ion batteries, ensuring the safety, durability, and sustainability of current systems is still a critical challenge. Solid polymer electrolytes (SPEs) have emerged as a safer and more durable alternative to the conventional liquid lithium-ion-battery electrolytes, offering additional benefits such as flexibility, ease of thin-film processing, and mechanical stability. To achieve high lithium-ion conductivity, good interfacial adhesion, and mechanical integrity, crosslinked rubbery polymers with low glass transition temperatures are often used as SPEs. However, their permanent crosslinks make them difficult to reprocess and recycle. To address these limitations, poly(β-amino ester) (PBAE)-based covalent adaptable networks (CANs) are prepared in this work as fully recyclable, catalyst-free, highly adhesive, and resilient SPEs. The adhesive and dynamic bond exchange characteristics, along with the lithium-ion conductivity of the PBAE CANs with varying crosslink densities, are systematically investigated. The obtained PBAE-CAN-based SPEs exhibit exceptional adhesive properties, recyclability, and an ionic conductivity of approximately 10⁻⁶ S/cm at room temperature. This conductivity can be further increased by an order of magnitude with the addition of a plasticizer. Long-term performance tests conducted at room temperature demonstrate stable operation for over 1,000 h without internal short circuits, attributed to the excellent creep recovery of the SPE at temperatures below the topology-freezing transition temperature where significant dynamic bond exchange begins to occur. Furthermore, full cell tests using LFP || Li configurations demonstrate the practical viability of the electrolyte, exhibiting stable rate performance and excellent capacity retention even after cycling at high C-rates. To further highlight its sustainability, the SPE is successfully reprocessed, allowing its smooth reuse. Furthermore, eco-friendly depolymerization and recovery of the lithium salt from the used PBAE CAN-based SPE are also demonstrated.