Morphology of nanoporous carbon-binder domains in Li-ion batteries—A FIB-SEM study

Abstract

FIB-SEM tomography is used to reconstruct the carbon-binder domain (CBD) of a LiCoO 2 battery cathode (3.9 × 5 × 2.3 μm 3 ) with contrast enhancement by ZnO infiltration via atomic layer deposition. We calculate the porosity inside the CBD (57.6%), the cluster-size distribution with a peak at 54 nm, and the pore-size distribution with a peak at 64 nm. The tortuosities of the pore space (1.6–2.0) and the CBD (2.3–3.5) show a mild anisotropy, which is attributed to the fabrication process. A comparison to a modeled homogenous CBD reveals that clustering in the CBD decreases its electronic conductivity while increasing the ionic diffusivity. To account for the higher calculated diffusivity compared to experimental values from literature, a simple binder swelling model is implemented, suggesting a swelling of 75 vol%. The prevention of both clustering and swelling could increase the volume available for active material and therefore the energy density. • The carbon-binder domain (CBD) of a commercial LiCoO 2 battery electrode is reconstructed via FIB-SEM tomography. • To enhance contrast, the binder is infiltrated with ZnO via chemical vapor deposition. • Calculated transport and morphological parameters feature anisotropy, most likely due to the fabrication process. • Simulation shows a CBD swelling of 75 vol% to match experimental ionic diffusivities from literature. • Preventing CBD clustering allows reduction of CBD volume and therefore an increase in energy density.