Post-synthetic Covalent Organic Framework to Improve the Performance of Solid-State Li⁺ Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Covalent organic frameworks (COFs) are crystalline materials with ordered channels suitable for ion transport.
• Functionalization of COFs can enhance their properties for specific applications like electrolytes.

Purpose of the Study:

• To design and synthesize a novel functionalized anionic COF, named COF-SS-Li, for use as a solid-state lithium-ion electrolyte.
• To investigate the lithium-ion transport mechanism and electrochemical performance of the synthesized COF.

Main Methods:

• Post-synthetic modification of BDTA-COF using the Povarov reaction to anchor sulfonate groups (-SO3-).
• Characterization of the COF-SS-Li material and evaluation of its ionic conductivity and electrochemical stability.
• Assembly and testing of lithium-ion battery cells using COF-SS-Li as the solid-state electrolyte.

Main Results:

• COF-SS-Li exhibits ionic conductivities of 9.63 × 10⁻⁵ S cm⁻¹ at 20 °C and 1.28 × 10⁻⁴ S cm⁻¹ at 40 °C.
• The material shows a wide electrochemical window of 4.85 V and stable cycling performance in Li|COF-SS-Li|Li symmetric cells for 600 h.
• A Li|COF-SS-Li|LiFePO₄ cell demonstrated an initial capacity of 117 mAh g⁻¹ and retained 56.7% after 500 cycles.

Conclusions:

• The functionalized anionic COF, COF-SS-Li, effectively promotes lithium-ion transport via a hopping mechanism.
• COF-SS-Li shows potential as a stable and efficient solid-state electrolyte for lithium-ion batteries.
• This research contributes to the development of advanced solid-state electrolytes for next-generation energy storage devices.