Influence of carbon binder domain on the performance of lithium-ion batteries: Impact of size and fractal dimension

Abstract

A lithium-ion battery (LIB) cathode comprises three major components: active material, electrical conductivity additive, and binder. The combination of binder and electrical conductivity additive leads to the formation of composite clusters known as the carbon binder domain (CBD) clusters. Preparation of a LIB cathode strongly influences the dispersion of the above-mentioned constituents leading to the formation of distinct pore and electrical conduction networks. The resulting structure thus governs the performance of LIBs. The presence of CBD is essential for the structural integrity and sufficient electrical conductivity of the LIB cathode. However, CBD abundance in LIB cathodes leads to unfavorable gravimetrical and volumetrical consequences owing to its electrochemical inertness. Increasing CBD content adds to the weight of the LIBs, thus negatively impacting the energy density. Furthermore, increased electrical conductivity is won at a cost of ionic conductivity as CBD clusters breach the pore networks in the cathode microstructure. The following study establishes a link between the various possibilities of CBD cluster size and fractal dimension that may eventualize during the mixing process of slurry preparation to the resulting microstructural properties and hence to the performance of LIBs by means of idealized cathode geometries. Since the performance determining processes occur at the microstructural scale, which are often very tedious to study via experimental research, the study makes use of spatially resolving microstructural, numerical, simulations. The results demonstrate that the CBD cluster size has a strong influence on the cathode microstructure. The CBD cluster fractal dimension on the other hand displayed a minor influence on the structural properties of the cathode, and the size of the cluster primary particles was shown to be the dominant factor. Finally, performance evaluation simulations confirmed the trends seen in structural properties with changing cluster size and fractal dimension.