Sodium-ion batteries (SIBs) are promising for large-scale energy storage, with hard carbon (HC) as a key anode material. Zeolitic imidazolate frameworks (ZIFs), particularly ZIF-8, are attractive HC precursors due to their tunable structure and porosity. However, conventional ZIF-8 synthesis methods are solvent-intensive, time-consuming, and difficult to scale. We aim to develop a scalable, eco-friendly synthesis route for ZIF-8-derived HC, enabling its use in high-performance SIB anodes.
To overcome the limitations of conventional synthesis methods, we adopted a quasi-solid-state approach using a twin-screw extruder, enabling large-scale (100–200 g/batch) and low-solvent production of ZIF-8.[1] This approach enhances the industrial feasibility of metal–organic framework (MOF)-derived carbons for energy storage applications. To optimize electrochemical performance, we reduced particle size via ball milling (from 50–100 µm to 0.5–10 µm) and increased surface area (from 350 m² g–1 to 900 m² g–1) through zinc leaching, possibly improving suitability for SIB anodes.
Despite a significant surface area increase, which typically leads to more solid–electrolyte interphase (SEI) formation and greater irreversible capacity loss, reversible capacity remained stable (259 mAh g–1 before and 257 mAh g–1 after zinc leaching. Although initial Coulomb efficiency dropped from 77.9% to 70.5%, the decline was milder than expected. Moreover, the acid-leached material exhibited good rate stability, retaining 65% of its capacity at 2C-cycling. These findings challenge the belief that high surface area in HCs leads to poor initial efficiency.
The results indicate that surface area is not the main factor responsible for the observed side reactions. Instead, features such as pore structure, surface chemistry, and how particles are connected may play
a more important role in keeping the SEI stable. This suggests that by carefully designing the microstructure of carbon materials, it is possible to reduce unwanted reactions and improve both capacity and initial efficiency, even when the surface area is high. Furthermore, the developed scalable route for ZIF-derived carbons is also of significant interest for a range of applications and shows particular promise in noble-metal-free electrocatalysis.
References:
[1] N. Y. Gugin, J. A. Villajos, O. Dautain, M. Maiwald, F. Emmerling, „Optimizing the Green Synthesis of ZIF-8 by Reactive Extrusion Using In Situ Raman Spectroscopy“, 2023
[2] S.-H. Wu, N. Y. Gugin, C. Prinz, A. Buzanich, J. Radnik, S. Dietzmann, D. Al-Sabbagh, S. Recknagel, P. Piehl, B. Mieller, H. Markötter, T. Lange, A. Rieck, C. Adam, F. Lindemann, J. Krug von Nidda, F. Emmerling, A. Mehmood, T.-P. Fellinger, „Sodium-ion battery research @ BAM (III): Eco-Friendly Large-Scale Synthesis of Carbon Anode Materials from Metal-Organic Frameworks for Sodium-Ion
Batteries“, 2025, in preparation.