Advancing Lithium-Ion Battery Manufacturing Sustainability through Microstructural Analysis of Composite Cathodes
Authors: Brenneis Willa , Liu Qingsong , Richards Jeffrey J. , Lopez Jeffrey 
Published: December 2024

To accelerate electric vehicle (EV) adoption and mitigate transportation emissions, lithium-ion battery (LIB) energy density and rate capability must be improved, advancing EV range and charging speed, respectively. The composite cathode is a major driver of these performance metrics, as its microstructure governs the flow of ions and electrons.1 Intentionally engineering cathode microstructure for efficient ionic transport will enable fast charging, thick cathodes for increased cell energy density. Here, while focusing our efforts on cathode design, we have the opportunity to prioritize sustainable manufacturing. We utilize our understanding of the slurry-cast cathode microstructure to facilitate the transition to solvent-free cathodes. Solvent-free cathode manufacturing promises advancements in performance, environmental safety, and economics, including increased cell energy density and reduced process toxicity, energy consumption and capital costs.2

In this presentation, I will first address relationships we have uncovered between slurry-cast cathode microstructure and resulting battery performance. We use a combination of small-angle neutron scattering (SANS), plasma focused ion beam scanning electron microscopy (PFIB-SEM), and electrochemical impedance spectroscopy (EIS) to elucidate the cathode microstructure in both dry and wet states, at the nanoscale, and over representative volumes. Using SANS, we see an expansion of carbon-binder domain (CBD) microstructure in the wet state and after calendaring. Further, we can deconvolute polymer binder and carbon black surface areas, allowing us to relate a decline in cycling performance to increased electrolyte-accessible carbon black in the CBD. We use these findings to inform the design of cathode microstructure for improved cycling stability.

Next, I will discuss how we apply our understanding of slurry-cast microstructures to dry-processed cathodes. The performance principles of dry-processed microstructures remain the same: they must efficiently conduct both lithium ions and electrons. However, the dry microstructure is vastly different than that of slurry-cast cathodes, and thus even less understood. We fabricate dry electrodes via the formation of binder fibers under applied shear, creating matrix with carbon fibers to support the active material particles. Utilizing binder fibers allows us to decrease the mass fraction of binder and increase the thickness of the cathode, increasing cell energy density. We apply the tools discussed here to understand the distinct dry microstructure and its impact on performance. Gaining a nanoscale understanding of both slurry-cast and dry-processed systems allows us to compare fundamental transport processes across various microstructures and manufacturing processes, informing future cathode design while advancing sustainability and reducing manufacturing cost.

References:

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Lu, Y. et al.
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5, 876–898 (2022).