Bridging the microstructural evolutions from slurry to porous electrode of a lithium-ion battery

Abstract

In lithium-ion batteries, the lithium-insertion particles that are responsible for the storage of charge are accommodated inside the porous electrodes. Although the architecture of a porous electrode is known to have a significant impact on the battery performance, there is still room to increase our knowledge about the quantitative links between electrode preparation steps and the resulting microstructural details. Here, a combination of the experimentation and physics-based modeling is employed to unravel the configurational translations of the particle aggregates from inside the slurry to the LiNi0.6Mn0.2Co0.2O2 porous electrodes. The solid-to-solvent ratio of the slurry is identified as a key parameter influencing the fractal dimension of the carbon-binder domain, drying-induced redistribution of the particles, and the compressibility behavior of the electrodes during the calendering step. The fundamental formalism introduced here paves the road for the development of optimal electrode architectures for lithium-ion cells by guiding the design of processing steps including slurry formulation and calendering. The porous electrodes are the crucial components of the modern electrochemical devices including lithium-ion batteries. The detailed configuration of the lithium-insertion, carbon black, and PVDF binder particles in a typical electrode of a lithium-ion cell has a significant impact on its energy and power density. A thinner electrode is desired to decrease the battery volume particularly for portable electronics and mobility applications. The thirst for longer discharge times, on the other hand, necessitates a higher loading of the Li-insertion particles inside the electrodes [1, 2]. A simultaneous fulfilling of these two wishes in a single design is a big challenge with a scope beyond the intrinsic charge-storage and transport properties of the individual components of the electrode. One needs to optimize the ionic and electronic connectivity of the Li-insertion particles in-and through-plane of the space confined between the current collector and separator [3-5]. A common practice is to decrease the thickness of the electrode under compression during the calendering step to optimize the effective electronic and ionic conductivity of the electrode. This is not a trivial task, however, considering the complexity and interplay among the processing steps involved in the preparation of a porous electrode, namely slurry formulation, mixing, coating, drying, and calendering (Fig. 1a-d). Our current quantitative and in-depth understanding of the interrelationships among these steps in determining the final microstructure of a porous electrode is very