Influence of particle properties on the processing of hard carbon anodes and nanostructured cathode materials for use in sodium-ion batteries


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Electrochemical storage is a key technology of the current century. In the future, electricity storage systems will become more important components of energy systems, especially for the upcoming electric mobility and for everyday use. Lithium-ion batteries (LIB) are currently the most important electrochemical energy storage devices. The largely mature technology is characterized by high gravimetric and volumetric energy densities. Sodium-ion-batteries (SIB) have the potential to replace lithium-ion-batteries (LIB) in some areas and to open up new fields of application. SIB could be one of the sustainable and environmentally friendly but also powerful and reliable storage systems, especially for medium and large energy storage systems. Furthermore, the advantages such as the availability of resources and the cost per watt-hour (Wh) make SIB attractive. The technology is already being investigated on a pilot scale, but is not yet industrially manufactured. As with LIB, energy storage is based on the principle of de- and intercalation of ions in host lattices.
In studies on the use of graphite as anode material in sodium-ion batteries, it shows a poor ability to intercalate sodium ions. According to current research, the poor intercalation properties of sodium in graphite are due to the formation energy of the intercalation compound. Currently, the most promising anode material for SIB is hard carbon. However, the specific capacity of this material depends on the particle properties, the slurry composition and the electrode processing. Within the process chain, the drying or the formation of the microstructure and the distribution of the slurry components play an important role.
On the cathode materials part, various possibilities are being investigated within the research cluster. Regardless of the material system, the production of nanostructured open-pore particles for the active materials is of great importance. Previous studies (e.g., IAM-ESS KIT) showed that nanoscale particles can be aggregated into larger nanoporous secondary particles by milling processes and subsequent calcination, which exhibited significantly better performance properties. The synthesized nanoporous NMC showed higher discharge capacities in half cells as well as better C-rate stability. The performance advantages are countered by lower adhesion forces to the arrestor film, which may be due to greater binder migration even into the nanoporous particles.

In this work, the mechanical and electrical properties of hard carbon electrodes for sodium ion batteries are investigated as a function of particle properties and drying conditions. The aim is an optimal distribution of the components in the electrode and the understanding of the formation depending on the process conditions. In particular, the focus is on developing a systematic relationship between slurry composition and drying conditions and the impact on electrode properties.
On the other hand, this work deals with the study of the processing of nanostructured particles. In particular, the focus is on the study of microstructure formation and component distribution as a function of drying conditions. The effect of binder migration at different drying rates on the mechanical, electrical and electrochemical properties of electrodes is analyzed.

This work contributes to the research performed at CELEST (Center for Electrochemical Energy Storage Ulm Karlsruhe) and Material Research Center for Energy Systems (MZE), it is funded by the German Research Foundation (DFG) under Project ID 390874152 (POLiS Cluster of Excellence).

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