Secondary-Phase Stochastics in Lithium-Ion Battery Electrodes

Abstract

Lithium-ion battery electrodes exhibit complex interplay among multiple electrochemically coupled transport processes, which rely on the underlying functionality and relative arrangement of different constituent phases. The electrochemically inactive solid phases (e.g., conductive additive and binder, referred to as the secondary phase), while beneficial for improved electronic conductivity and mechanical integrity, may partially block the electrochemically active sites and introduce additional transport resistances in the pore (electrolyte) phase. In this work, the role of mesoscale interactions and inherent stochasticity in porous electrodes is elucidated in the context of short-range (interface) and long-range (transport) characteristics. The electrode microstructure significantly affects kinetically and transport-limiting scenarios and thereby the cell performance. The secondary-phase morphology is also found to strongly influence the microstructure-transport-kinetics interactions. Apropos, strategies have been proposed for performance improvement via electrode microstructural modifications.

Resolving the Discrepancy in Tortuosity Factor Estimation for Li-Ion Battery Electrodes through Micro-Macro Modeling and Experiment

“…This simplification has been well-established in the LIB literature. [1][2][3][4][5][6] With disparate CBD and active material particle sizes and morphologies, the resulting electrode contains a complex network of pores ranging from nanometer to micrometer length scales. Electrode battery macro-homogeneous electrochemical models often use porous electrode theory and thus abstract microstructural heterogeneity of composite electrodes using effective macroscopic properties.…”

“…However, given the algorithmic nature of these approaches, a generated CBD phase is not necessarily realistic. To circumvent these imaging limitations, this work uses a physics-based CBD phase description recently proposed by Mistry et al, 6 which accounts for necessary evaporation dynamics that govern the interfacial arrangement of the CBD phase to generate a plausible CBD geometry within the pore domain. The method reasonably predicts effective properties as well as performance trends.…”

Electrode Mesoscale as a Collection of Particles: Coupled Electrochemical and Mechanical Analysis of NMC

“…Mesoscale modeling is commonly used to predict the effective electrical conductivity of the electrode for macroscale modeling [63], treating the effective conductivity as a static parameter. Recent works [19,21,22] have recognized that the CBD conductivity changes as a function of lithiation due to the mechanical forces generated from lithiation.…”

“…One important factor missing from much of the current mesoscale simulation literature is an accurate representation of the PVDF and carbon black composite binder domain (CBD) phase [53,63]. Experiments have shown that CBD has a significant impact on electrode performance [64][65][66][67][68].…”

“…Other approaches to image the binder suffer from small fields of view or are only 2D, limiting their direct use at the mesoscale [30,33,[71][72][73][74][75]. Therefore, the most advanced image-based mesoscale simulations use algorithms to reconstruct the CBD phase atop particle phases derived from images [19,21,63,[76][77][78]. There is not yet a consensus approach to reconstructing the CBD phase morphology, even though predictions have been shown to be sensitive to this morphology [21].…”