A Combination of X‐Ray Tomography and Carbon Binder Modeling: Reconstructing the Three Phases of LiCoO₂ Li‐Ion Battery Cathodes

Abstract

X‐ray tomography allows the active‐material domain (LiCoO2) of Li‐ion battery cathodes to be imaged, but it is unable to resolve the carbon‐binder domain (CBD). Here, a new method for creating a complete 3D representation (virtual design) of all three phases of a cathode is provided; this includes the active‐material domain, the CBD, and the electrolyte‐filled pore space. It combines X‐ray tomographic data of active material with a statistically modeled CBD. Two different statistical CBD morphology models are compared as examples: i) a random cluster model representing a standard mixture of carbon black and polyvenylidene fluoride (PVDF) and ii) a fiber model. The transport parameters are compared in a charged and a discharged cathode. The results demonstrate that the CBD content and morphology changes the ionic and electronic transport parameters dramatically and thus cannot be neglected. Calculations yield that the fiber model shows up to three times higher electrical conductivity at the same CBD content (discharged case) and better ionic diffusion conditions for all CBD contents. In the charged case, the morphology impact on electrical conduction is small. This effective method to generate transport parameters for different CBDs can be transferred to other CBD morphologies and electrodes.

Influence of Electrode Density on the Performance of Li-Ion Batteries: Experimental and Simulation Results

“…HD electrodes have higher volume fraction of CBDs in the pore space resulting in better binding and conduction between the particles. These two effects should decrease the overall cell impedance, however the magnitude of the effect depends on the nature of the AM and CBDs [15].…”

“…; however, these additives have a large surface area, which could lead to parasitic reactions with electrolytes [14]. The use of more fiber shaped carbons instead of more spherical Carbon Black (CB) enhances percolating properties of the electrode matrix [15].…”

“…It presents an opportunity for cell manufacturers to tune their cell performance. Especially for badly conducting AM, the influence of binders and conductive agents can be very influential [15].…”

“…• Electric conduction in the matrix of the porous electrode-depending on the intrinsic conductivity of the AM, this electronic current is mostly carried by the carbon-binder domain (CBD) [15].…”

Three-Dimensional Visualization of Gas Evolution and Channel Formation inside a Lithium-Ion Battery

“…25 Due to the high fluxes generated by synchrotron sources, synchrotron X-ray imaging has evolved into a powerful characterization tool in the field of materials science. [26][27][28][29][30][31][32][33][34][35][36] Especially synchrotron X-ray tomography has enabled researchers to obtain unprecedented insights into LIBs from the level of individual particles to the scale of entire electrodes. [37][38][39][40] Most recently, Ebner et al, have directly observed and quantified electrochemical and mechanical degradation in a SnO anode.…”