Alternating-sequence polymer chain facilitating Li⁺ transport in covalent organic frameworks

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Covalent organic frameworks (COFs) are promising solid-state electrolytes due to their tunable properties.
• Current COF electrolytes suffer from low ionic conductivity and poor lithium-ion transference numbers, hindering battery applications.
• Effective strategies for pore chemical environment modulation are needed to optimize ion transport.

Purpose of the Study:

• To develop a pore-engineering strategy for COF-based solid-state electrolytes.
• To enhance ionic conductivity and lithium-ion transference number in COFs.
• To improve the performance and stability of solid-state lithium batteries.

Main Methods:

• Incorporation of alternating oxyethylene and perfluoroalkyl chains into COFs.
• Sequence-controlled modification of COF pore environments.
• Fabrication and testing of symmetric Li|Li and solid-state Li|NMC batteries.

Main Results:

• Achieved high Li+ conductivity (1.06 mS·cm⁻¹) and Li+ transference number (0.9).
• Demonstrated excellent Li plating/stripping stability (>7500 hours) in symmetric cells.
• Solid-state batteries showed high capacity (180 mAh·g⁻¹ at 1C) and long-term cycling stability (80% retention after 700 cycles at 5C).

Conclusions:

• Pore engineering by incorporating specific chains effectively enhances ion transport pathways in COFs.
• The developed COF electrolytes significantly improve solid-state lithium battery performance, enabling fast charging and long cycle life.
• This strategy opens new avenues for designing high-performance solid-state electrolytes.