X‐Ray Tomography of Porous, Transition Metal Oxide Based Lithium Ion Battery Electrodes

Abstract

We report the use of synchrotron radiation X-ray tomographic microscopy (SRXTM) to obtain statistically signifi cant volume ( ∼ 700 × 700 × 70 μ m 3 ) 3D reconstructions of porous electrode microstructures of transition metal oxide based electrodes. [ 1 ] We implement a segmentation algorithm that allows identifi cation of individual particles and validate it by showing that the calculated particle size distribution (PSD) is in agreement with experimentally determined PSD obtained with laser diffraction. We study the microstructure of LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC)-based cathodes, prepared with varying weight percent of carbon black and binder (2-5 wt%) and different compressions (0-2000 bar), and their electrochemical performance. Tomographic data (raw and processed with particles identifi ed and labeled) and the corresponding electrochemical data for 16 different cathodes is provided open source. [ 2 ] The microstructure datasets can be used to study electrode properties like porosity, tortuosity, electrode anisotropy, and homogeneity, or as realistic geometries for three dimensional (3D) electrochemical simulations. The electrochemical data is intended to aid in the verifi cation of simulation models. The large number of studied particles (approx. 7000-19000 per electrode) allows us to investigate spatially resolved PSD and shows that the vicinity of electrode boundaries is populated by smaller particles than the bulk electrode. In addition to insight into electrode morphology, we demonstrate that the technique is capable of resolving features on the sub-particle level such as particle fracture, which is observed here under high compression conditions. It is becoming increasingly clear that the development of next generation, higher performance lithium ion batteries (LIB) will require a concerted effort between experimentalists and simulation experts. In addition to the development of predictive tools for the selection of active materials, realization of LIBs with high C-rate capabilities and energy density will require the development of roadmaps for achieving favorable porous electrode microstructures. [ 3 , 4 ] However, due to the lack of publically available microstructural data on porous electrodes to date, there exists a disconnect between the experimental and simulation communities. The simulation community, despite significant advances in computation over the past decades, must rely on simplifi ed pictures of porous electrode microstructure or computer generated microstructures that bear an as-of-yet unquantifi ed relationship to real battery microstructures.While one-dimensional (1D) simulations are appealing for their simplicity and computational effi ciency, there are significant limitations. Newman-type models rely on the representation of the electrode's complexity by effective medium approximations. [ 5 ] For systems featuring a broad PSD, as often found in real LIB electrodes, the validity of the Bruggeman relation, which is widely used to estimate the electrode's tortuosity from porosity, ha...

Tortuosity in electrochemical devices: a review of calculation approaches

“…In total, 16 LiNi1/3Mn1/3Co1/3O2 battery electrodes with varying weight ratios were manufactured and reconstructed using X-ray synchrotron tomography. 56 Tortuosity was then extracted by simulating mass transport according to Fick's law across the sample volume (see section 5.2). It was shown, that calculated tortuosity values always lie slightly above the Bruggeman correlation.…”

“…55 Continuing work in the field of battery research from Wood and co-workers (cf. 53,55,56 57 and has been recently applied in practice. 58 This approach is similar to stereological methods which quantify 3D properties based in 2D image slices.…”

Quantifying Inhomogeneity of Lithium Ion Battery Electrodes and Its Influence on Electrochemical Performance

“…Experimental X-Ray tomographic miroscopy and data binarization.-For each of the four anodes, X-ray tomographic microscopy (XTM) 16 Figure 1a. They reveal different types of graphite particles (the active particles in electrode I, III, and IV are flake-like while electrode II consists of spherical graphite) with varying size distributions and resulting microstructures.…”

Chemomechanics of ionically conductive ceramics for electrical energy conversion and storage

“…A variety of tomographic methods have been applied to battery electrodes to better understand these complex heterogeneous microstructures by facilitating evaluation of porosity, tortuosity, and surface area, and to inform more realistic models of electrode function and failure. X-ray tomography has been used to non-destructively reconstruct composite electrodes [39,40] [42,43]. Clague et al converted this 3-D structure into a mesh for finite element (FE) simulation of stresses developing within the material as temperature increased.…”