Functional Separator Enabled by Covalent Organic Frameworks for High-Performance Li Metal Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Lithium dendrite growth and unstable solid electrolyte interphase (SEI) films impede lithium metal battery (LMB) development.
• Uncontrolled ion transport is a primary cause of dendrite formation.

Purpose of the Study:

• To design a dual-functional battery separator that modulates ion transport and SEI film formation.
• To suppress lithium dendrite growth and enhance the stability of lithium metal anodes.

Main Methods:

• Fabrication of a composite separator (COF@PP) by adhering TpPa-2SO3H covalent organic framework (COF) nanosheets onto cellulose nanofibers (CNF) on a polypropylene separator.
• Electrochemical testing of Li//COF@PP//Li symmetric cells and LiFePO4//Li cells.

Main Results:

• The COF@PP separator demonstrated stable cycling over 800 hours in symmetric cells.
• Fast lithium ion transport kinetics and suppressed dendrite growth were observed.
• LiFePO4//Li cells with the COF@PP separator achieved a high discharge capacity of 109.6 mAh g⁻¹ at 3 C with excellent cycle stability.
• A robust LiF-rich SEI film was induced by the COFs, enhancing performance.

Conclusions:

• The COF@PP composite separator effectively addresses key challenges in LMBs.
• This dual-functional separator promotes stable lithium plating/stripping and improves overall battery performance.
• The developed COF-based separator is a promising candidate for advancing the practical application of lithium metal batteries.