Stablized PEO/covalent organic framework hybrids with improved Li+ transfer capability for solid state lithium metal batteries

Abstract

Polyethylene oxide (PEO) electrolytes are widely used in lithium metal batteries (LMBs) due to their high safety and good flexibility. However, poor ion transport performance and interfacial stability limit its practical application. In this study, a covalent organic polymer (CPTP) was designed as a multifunctional material to be combined with PEO-based electrolytes for the preparation of a high-performance solid polymer electrolyte. The addition of CPTP promotes the dissociation of lithium salt through the C=N sites in the structure, and reduces the crystallinity of PEO to provides additional lithium transport pathways, thus enhancing the kinetics of lithium ion migration. More importantly, CPTP significantly enhances the interfacial stability of PEO/CPTP composite electrolyte/Li anode, promoting the formation of a stable SEI layer on the surface of the lithium metal electrode. The PEO/CPTP electrolyte has a lithium ion migration number of 0.59, and the Li//PEO/CPTP//Li batteries can stably operate for more than 1000 h with a polarization voltage of less than 0.2 mV. The fabricated all-solid-state Li//PEO/CPTP//LiFePO₄ lithium metal batteries can run 300 cycles with 81 % capacity reservation at 0.2 C, which could ascribe to the regulat phase stability in lithium metal batteries.