Donor-Acceptor Porous Aromatic Framework Cathode with Fast Redox Kinetics for Ultralow-Temperature (-70 °C)...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Low-temperature rechargeable batteries are critical for cryogenic energy storage.
• Inorganic electrode materials suffer from slowed kinetics and mechanical instability at low temperatures, leading to capacity degradation.
• Developing stable electrode materials for low-temperature operation remains a significant challenge.

Purpose of the Study:

• To design and synthesize a novel porous aromatic framework (PAF-310) for enhanced low-temperature electrochemical performance.
• To investigate the charge transport acceleration and reaction kinetics facilitation of PAF-310 at cryogenic conditions.
• To elucidate the ion storage mechanism in PAF-310 for low-temperature potassium ion batteries (PIBs).

Main Methods:

• Synthesis of a donor-acceptor (D-A) porous aromatic framework (PAF-310) using phenazine (p-type) and hexaazatrinaphthylene (n-type) building blocks.
• Electrochemical performance testing of PAF-310 as a cathode material for PIBs at various temperatures (25°C down to -70°C).
• In/ex-situ spectral characterizations and theoretical calculations to understand the ion storage mechanism.

Main Results:

• PAF-310 exhibited excellent electrochemical performance at 25°C, with a discharge specific capacity of 215.6 mAh g⁻¹ at 0.2 A g⁻¹ and outstanding rate capability (77.8 mAh g⁻¹ at 50 A g⁻¹).
• Impressive specific capacities were maintained at low temperatures: 168.2 mAh g⁻¹ at -20°C and 130.1 mAh g⁻¹ at -40°C (at 0.2 A g⁻¹).
• Even at -70°C, PAF-310 retained good specific capacity (102.2 mAh g⁻¹ at 50 mA g⁻¹), demonstrating remarkable low-temperature stability.
• Continuous co-storage mechanism of K⁺ and PF₆⁻ ions was elucidated.

Conclusions:

• Constructing a D-A porous aromatic framework (PAF-310) effectively accelerates charge transport and facilitates reaction kinetics at low temperatures.
• PAF-310 demonstrates superior electrochemical performance and stability for low-temperature potassium ion batteries compared to existing materials.
• This work presents a viable molecular design strategy for developing stabilized low-temperature PIBs.