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

Intercalated metal-organic frameworks (iMOFs) based on aromatic dicarboxylate are appealing negative electrode active materials for Li-based electrochemical energy storage devices. They store Li ions at approximately 0.8 V vs. Li/Li+ and, thus, avoid Li metal plating during cell operation. However, their fast-charging capability is limited. Here, to circumvent this issue, we propose iMOFs with multi-aromatic units selected using machine learning and synthesized via solution spray drying. A naphthalene-based multivariate material with nanometric thickness allows the reversible storage of Li-ions in non-aqueous Li metal cell configuration reaching 85% capacity retention at 400 mA g(-1) (i.e., 30 min for full charge) and 20 degrees C compared to cycling at 20 mA g(-1) (i.e., 10 h for full charge). The same material, tested in combination with an activated carbon-based positive electrode, enables a discharge capacity retention of about 91% after 1000 cycles at 0.15 mA cm(-2) (i.e., 2 h for full charge) and 20 degrees C. We elucidate the charge storage mechanism and demonstrate that during Li intercalation, the distorted crystal structure promotes electron delocalization by controlling the frame vibration. As a result, a phase transition suppresses phase separation, thus, benefitting the electrode's fast charging behavior. Ideal anode materials for Li-ion capacitors must demonstrate safety and fast-charging properties. Here, the authors propose intercalated metal-organic frameworks for fast-charging Li-ion capacitors using a combined machine learning design and spray-dry synthesis.

Automated summary

Intercalated metal-organic frameworks (iMOFs) synthesized via spray drying and machine learning design are proposed as fast-charging materials for Li-ion capacitors, demonstrating high capacity retention and electrochemical performance.