Highly Conductive Imidazolate Covalent Organic Frameworks with Ether Chains as Solid Electrolytes for Lithium Metal...

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Poly(ethylene oxide) (PEO)-based electrolytes are widely used for lithium-ion (Li+) conduction due to efficient salt dissociation.
• Limitations of PEO electrolytes include chain entanglement and restricted ion diffusion pathways, hindering their use in advanced batteries.
• Ionic covalent organic frameworks (iCOFs) offer ordered structures that facilitate rapid Li+ transport, addressing PEO limitations.

Purpose of the Study:

• To synthesize and characterize novel imidazolate covalent organic frameworks (COFs) with methoxyethoxy side chains for solid-state electrolytes.
• To evaluate the electrochemical performance of these iCOFs, specifically their Li+ conductivity and transference number.
• To assess the interfacial stability of the iCOFs with lithium metal and their performance in LiFePO4 batteries.

Main Methods:

• Synthesis of PI-TMEFB-COFs via Debus-Radziszewski multicomponent reactions.
• Ionization to form Li+@PI-TMEFB-COFs.
• Electrochemical characterization including conductivity measurements, transference number determination, and battery cycling tests.

Main Results:

• Li+@PI-TMEFB-COFs exhibit high Li+ conductivity (8.81 mS cm-1) and a high transference number (0.974).
• Methoxyethoxy chains facilitate Li+ dissociation and transport through the COF pores, forming a stable interface with Li metal.
• LiFePO4 batteries assembled with Li+@PI-TMEFB-COFs show an initial discharge capacity of 119.2 mAh g-1 at 0.5 C, with 82.0% capacity retention after 400 cycles.

Conclusions:

• Imidazolate COFs with ether chains synthesized via multicomponent reactions represent a promising class of solid electrolytes.
• These iCOFs overcome the limitations of traditional PEO electrolytes, offering efficient ion transport and stable interfaces.
• The findings open new avenues for developing advanced rechargeable batteries utilizing iCOF-based solid electrolytes.