Michael Baunach

Delamination behavior of lithium-ion battery anodes: Influence of drying temperature during electrode processing

ABSTRACT One essential process step during electrode processing for lithium-ion batteries is the drying of the wet particulate electrode coating. The electrode film solidifies during evaporation of the solvent and a porous film is formed. In this study, we focus on the influence of drying temperature on the internal electrode structure of the dry film. Anode slurries that consist of graphite and an aqueous binder system were coated and subsequently dried. To assure defined and controllable drying conditions, a laboratory set-up with a temperature-controlled substrate carrier and an impingement dryer was used. To facilitate a scale-up to continuously passed dryers, the choice of experimental temperatures was based on a calculation of steady-state temperatures that result from gas temperatures that are commonly applied in industrial drying processes. The delamination behavior of the differently dried electrodes was investigated by means of a 90° peel test. The results show a strong dependency of electrode adhesion on drying temperature. A lower adhesion force at higher temperatures hints at a variation in binder content at the interface between the copper substrate and the coating layer. The formation of a consolidation layer at the air-film interface during drying is identified as a possible explanation and a criterion for consolidation layer formation is suggested.

Development of a three-stage drying profile based on characteristic drying stages for lithium-ion battery anodes

ABSTRACT Based on the state of current research on battery electrode drying, a custom drying profile design is proposed and validated. It allows for drying time reduction, while the anodes’ mechanical integrity is maintained. In a tripartite process, the deterioration of the active layer adhesion to the substrate that is typically observed for increased drying rates is prevented through adjusting mild drying conditions in an intermediate drying stage. This stage is confined by two high drying rate stages which allow for reduction of the total drying time by about 40% compared to a reference drying process.

Experimental investigation into battery electrode surfaces: The distribution of liquid at the surface and the emptying of pores during drying

HYPOTHESIS Drying constitutes a key step in the production of thin, particulate films as the complex microstructure develops and functional additives redistribute throughout the film, thus shaping the film properties. The onset of pore emptying constitutes a paramount marker in the film formation process as capillary liquid transport emerges. EXPERIMENTS Film shrinkage, development of surface liquid content and liquid depletion in surface pores of thin films are studied by means of a novel experimental approach, using the example of lithium-ion battery anodes. An optical brightener is incorporated into the films, which are produced in a convective slot-nozzle dryer. After various drying times, images of the film, which emit light fluorescently during exposure to UV-A radiation, are captured and analyzed by image processing. Film shrinkage is observed by means of a laser displacement sensor. FINDINGS As soon as the first pores empty, pore fluid is transported convectively. By exerting an external force, i.e. a pressure surge, on the film, the transition from a fully saturated to a partially emptied film is revealed. The significance of drying rate and particle shape are studied. We show that liquid depletion in surface pores can occur both prior and concurrent with the end of film shrinkage.

Impact of drying conditions and wet film properties on adhesion and film solidification of lithium-ion battery anodes

ABSTRACT Electrodes constitute a vital component of lithium-ion battery cells. The property-determining, porous microstructure of anodes, which is composed of micrometer-sized graphite particles and nanoscale additives, was developed during convective removal of the solvent. In the present work, the impact of significant drying conditions and wet film properties, such as drying rate, slurry composition or active material particle size, just to name a few, is examined to provide further understanding of film solidification. The influence on both adhesion and film solidification is investigated. Subsequently, a previously developed film solidification mechanism will be critically reviewed based on findings.