Application and Comparison of Different Structuring Concepts for Ultra-Thick NMC 622 Cathodes in High Energy Lithium Ion Batteries

Abstract

For future Lithium-ion battery applications such as electric vehicles, the battery manufacturing costs and their energy density are key limiting factors that have to be improved, in order to open this technology for a broader market. To address both challenges at once, one promising strategy is to increase the mass loading of state of the art electrodes to extreme values, thus, yielding ultra-thick electrodes. This approach allows to reduce the amount of passive materials in the cell stack in favor of more active material.[1,2] However, an increase in electrode film thickness is usually associated with a variety of drawbacks such as lower rate capability and higher mechanical stress during drying and processing.[3,4] In this contribution, different concepts to overcome these drawbacks are presented and compared. Ultra-thick NMC 622 cathodes with a mass loading of 50 mg/cm2 (≈ 8 mAh/cm2) were prepared and the influence of different manufacturing processing steps (mixing, drying and calendaring) on the electrochemical properties of these electrodes was investigated. Furthermore, the electrode architecture was optimized by pursuing different structuring strategies, in order to improve the Lithium-ion transport. Firstly, the introduction of electrolyte channels by pore-forming agents and electrode perforation is evaluated. Secondly, a multilayer design is explored[5], whereby local porosity and active material particle sizes can be controlled specifically. Finally, the electrolyte concentration was shown to have a significant influence on the electrochemical performance of ultra-thick electrodes and advantageous structures are identified by 3D microstructure resolved simulations based on stochastic structure models, which were calibrated to tomographic image data.[6–8] By application of combined processing and structuring measures, the specific discharge capacity of ultra-thick cathodes at 8 mA/cm2 (≈ 1C) was enhanced by more than 60%. Acknowledgement: The presented work was financially supported by BMBF within projects HighEnergy and PRODUKT under the reference numbers 03XP0073 and 03XP0028.