The Effect of Carbon Black Aggregation on Lithium Ion Cathode Performance
Authors: Morelly Samantha , Alvarez Nicolas J. , Tang Maureen 
Published: February 2020

Current processing standards for battery electrode slurries are determined through time-, labor-, and capital-intensive trial and error. The effect of these processing conditions on battery performance is acknowledged, but not fully understood. The field of rheology, specifically the study of colloidal suspensions, holds a wealth of knowledge about the particle-particle interactions that develop in fluids very similar to battery electrode slurries. Our work uses rheology to measure and understand changes in the viscoelastic properties of battery slurries as a function of mixing parameters, and then utilizes these changes as indicators of the final battery performance and structure. We are, more specifically, interested in the dry mixing of conductive additive and active material, due to its documented ability to change the battery slurry’s viscoelastic behavior, e.g. the potential to change the slurry from a colloidal gel to viscoelastic fluid [1,2].

Slurry microstructure is argued to have a large impact on battery performance due to the persisting structure (particle dispersion) during the subsequent processing steps. Dry-mixing is thought to impact battery performance by depositing conductive additive on the surface of the micron-sized active material, increasing overall electronic conductivity of the electrode. The goal of this work is to decouple whether increased electronic conductivity, the initial electrode microstructure (particle dispersion), or a synergism of the two is responsible for increases in battery performance. By keeping the total concentration of carbon constant, we generate electrode slurries with different degrees of free carbon, i.e. carbon that can form a volume spanning colloidal network (colloidal gel). The different degrees of microstructure and carbon deposited on the active material will determine if there exists an optimum in battery performance.

Our initial work investigates the extremes of dry-mixing. This has allowed us to investigate systems where all of the available carbon is free to aggregate and form a gel network (long-range electron pathways) and all of the available carbon has been deposited onto the active material (short-range electron pathways). This has allowed us to effectively decouple the individual impacts of short-range and long-range electron pathways on battery performance. Rate capability tests of batteries made from each system show that long-range electron pathways have a greater beneficial impact than short-range pathways. These initial findings in terms of short- and long-range electron pathways run contrary to current literature findings [1,2], which have indicated that improvement of short-range electron pathways is needed for improved performance. Our future work will investigate methods to optimize these short-range contacts while maintaining the beneficial long-range contacts that we have observed.

[1]W. Bauer, D. Noetzel, Ceram. Int. 40 (2014) 4591.

[2]G.-W. Lee, J.H. Ryu, W. Han, K.H. Ahn, S.M. Journal of Power Sources 195 (2010) 6049–6054.