Enhancing ionic conductivity and suppressing Li dendrite formation in lithium batteries using a vinylene-linked covalent organic framework solid polymer electrolyte

Abstract

The growing demand for energy-dense and safe batteries drives research towards all-solid-state lithium (Li) batteries. Existing poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) suffer from low Li⁺ conductivity and Li dendrite penetration. Covalent organic frameworks (COFs) as highly crystalline, porous, and chemically diverse organic materials show great potential to address these problems. However, extensively studied imine-linked COFs show insufficient electrochemical stability against reactive Li metal, limiting their application for Li batteries. Herein, we develop a chemically stable vinylene-linked covalent organic framework (VCOF)-based SPE. By incorporating <4 wt% VCOF-1, a 25% improvement in ionic conductivity and a 46% increase in Li⁺ transference number at 60 °C are achieved. DFT calculations reveal that VCOF-1 facilitates Li⁺ transport through its cylindrical pores aided by PEO. In situ X-ray tomography confirms that VCOF-1 substantially suppresses Li dendrite growth in the VCOF-SPE-based Li metal batteries attributed to the enhanced Li-ion conduction and 12-fold improved mechanical strength. VCOF-SPEs also exhibit a high capacity of ∼145 mA h g⁻¹ at 0.1C in LiFePO₄|Li coin cells. Notably, the LiFePO₄|Li pouch cell withstands abuse test conditions such as folding, cutting, and nail penetration. These results demonstrate the potential of VCOFs in future all-solid-state Li metal batteries for energy storage.