Heterogeneous intercalated metal-organic framework active materials for fast-charging non-aqueous Li-ion capacitors

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Intercalated metal-organic frameworks (iMOFs) are promising negative electrode materials for Li-based energy storage due to their low operating voltage (~0.8 V vs. Li/Li+), which prevents lithium plating.
• A key limitation of current iMOFs is their insufficient fast-charging capability, hindering their practical application.

Purpose of the Study:

• To develop novel iMOFs with enhanced fast-charging performance for Li-ion batteries.
• To utilize machine learning for the rational design and selection of iMOF materials with multi-aromatic units.
• To synthesize and characterize these advanced iMOFs for electrochemical energy storage.

Main Methods:

• Machine learning algorithms were employed to screen and select multi-aromatic units for iMOF design.
• Naphthalene-based iMOFs with nanometric thickness were synthesized using solution spray drying.
• Electrochemical performance was evaluated in non-aqueous Li metal cells and full cells with activated carbon cathodes, focusing on capacity retention at high charge/discharge rates.

Main Results:

• A synthesized naphthalene-based iMOF demonstrated excellent Li-ion storage, retaining 85% capacity at 400 mA g-1 (30 min full charge) compared to 20 mA g-1 (10 h full charge).
• In a full cell configuration, the iMOF material achieved 91% discharge capacity retention after 1000 cycles at 0.15 mA cm-2 (2 h full charge).
• The charge storage mechanism was elucidated, revealing that a distorted crystal structure enhances electron delocalization and suppresses phase separation, thereby improving fast-charging behavior.

Conclusions:

• Machine learning-guided design and solution spray drying synthesis of iMOFs enable superior fast-charging capabilities in Li-ion batteries.
• The developed naphthalene-based iMOF materials offer a promising pathway for next-generation high-power energy storage devices.
• Understanding the structure-property relationship, particularly the role of crystal distortion in electron delocalization, is crucial for optimizing electrode performance.