Mechanisms of Li-Ion Transport in Two-Dimensional Covalent Organic Framework-Polyethylene Glycol Composite Electrolytes

Abstract

Understanding the mechanisms of Li-ion transport in two-dimensional covalent organic frameworks (2D COFs) is essential for the rational development of these solid-state electrolytes in metal batteries. However, as 2D COFs are frequently used in composition with other materials, elucidating the Li-ion transport mechanisms in such complex structures has proven challenging. Here, we employed 309 submicrosecond atomistic molecular dynamics simulations to unravel the intricacies of microscopic conformations and Li-ion transport mechanisms in a representative COF-5 and polyethylene glycol (PEG) composite electrolyte under experimental conditions. We identified 13 distinct Li-ion transport modes, providing detailed insights into the mechanisms governing Li-ion transport in 2D COF-based composite electrolytes and the effects of component ratios and temperature. At high temperatures, the 2D COF promotes intrachain Li-ion movement while suppressing interchain hopping, thereby reducing ionic motion. Conversely, at low temperatures, the 2D COF enhances the kinetics of PEG chains, facilitating vehicle Li-ion movement and resulting in accelerated ion transport. These findings highlight the unique Li-ion transport mechanisms in 2D COF-polymer composites, distinguishing them from conventional polymer electrolytes. This work establishes a comprehensive theoretical framework for describing Li-ion transport in 2D COF-based electrolytes and provides a valuable reference for the rational design of next-generation solid-state electrolytes for advanced energy storage applications.