Design of Isomeric Covalent Organic Frameworks for Realizing Low-Temperature Sodium Storage

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Low-temperature sodium-ion batteries (SIBs) are crucial for energy storage in extreme environments.
• Sluggish reaction kinetics, slow ionic diffusion, and lattice shrinkage hinder SIB performance at low temperatures.

Purpose of the Study:

• To design high-performance low-temperature SIBs using anthraquinone-based covalent organic frameworks (COFs).
• To optimize sodium storage by engineering the spatial arrangement of carbonyl groups in COFs.

Main Methods:

• Isomeric design strategy for anthraquinone-based COFs (TPAQ-COF) to create adjacent carbonyl coordination sites (i-TPAQ-COF).
• Electrochemical performance testing at various temperatures and cycling conditions.
• Molecular dynamics (MD) simulations and density functional theory (DFT) calculations to elucidate the mechanism.

Main Results:

• i-TPAQ-COF achieved a reversible capacity of 153 mAh g⁻¹ at 0.1 A g⁻¹ and 95% retention after 5000 cycles at 2 A g⁻¹.
• Remarkable low-temperature performance: 124 mAh g⁻¹ at -30°C (82% of room-temperature capacity) and 114 mAh g⁻¹ at -40°C (75% of room-temperature capacity).
• MD and DFT revealed that adjacent carbonyl groups provide a synergistic chelation effect, enhancing discharge voltage, sodium ion capture, and ion transport.

Conclusions:

• The isomeric design strategy effectively optimizes sodium storage in COFs for low-temperature SIBs.
• i-TPAQ-COF demonstrates superior electrochemical performance and excellent low-temperature resilience.
• The synergistic chelation effect is key to improving ion kinetics and battery performance in extreme conditions.