A Phosphine-Amine-Linked Covalent Organic Framework with Staggered Stacking Structure for Lithium-Ion Conduction

Area of Science:

• Materials Science
• Chemistry
• Solid-State Ionics

Background:

• Two-dimensional (2D) materials offer potential for flexible electronics due to in-plane ionic conduction.
• Exfoliating 2D covalent organic frameworks (COFs) is challenging due to strong π-stacking interactions.
• Developing easily delaminated COFs is crucial for creating advanced solid electrolytes.

Purpose of the Study:

• To synthesize a novel phosphine-amine-linked 2D COF.
• To investigate the exfoliation properties of the synthesized COF.
• To evaluate the potential of the exfoliated COF as a solid electrolyte material.

Main Methods:

• Nucleophilic substitution reaction of phosphazene with amines to synthesize the 2D COF.
• Characterization of the COF's crystalline structure and stacking arrangement (AB-staggered).
• In situ post-quaternization for improved ionization and subsequent layered exfoliation.

Main Results:

• A crystalline phosphine-amine-linked 2D COF with AB-staggered stacking was successfully synthesized.
• The interlocked P-Cl bonds facilitate delamination of non-interlocked layers, enabling exfoliation.
• The ultrathin nanosheets effectively decouple lithium salts, leading to fast solid-state ion transport with high conductivity and low activation energy.

Conclusions:

• The P-N substitution reaction is a viable route for COF crystallization.
• Staggered stacking in 2D COFs can be engineered for facile exfoliation.
• These exfoliated 2D COFs show promise for designing high-performance solid electrolytes for flexible electronics.