Enhanced Imaging of Lithium Ion Battery Electrode Materials

Abstract

In this study we present a novel method of lithium ion battery electrode sample preparation with a new type of epoxy impregnation, brominated (Br) epoxy, which is introduced here for the first time for this purpose and found suitable for focused ion beam scanning electron microscope (FIB-SEM) tomography. The Br epoxy improves image contrast, which enables higher FIB-SEM resolution (3D imaging), which is amongst the highest ever reported for composite LFP cathodes using FIB-SEM. In turn it means that the particles are well defined and the size distribution of each phase can be analyzed accurately from the complex 3D electrode microstructure using advanced quantification algorithms. The authors present for the first time a new methodology of contrast enhancement for 3D imaging, including novel advanced quantification, on a commercial Lithium Iron Phosphate (LFP) LiFePO 4 cathode. The aim of this work is to improve the quality of the 3D imaging of challenging battery materials by developing methods to increase contrast between otherwise previously poorly differentiated phases. This is necessary to enable capture of the real geometry of electrode microstructures, which allows measurement of a wide range of microstructural properties such as pore/particle size distributions, surface area, tortuosity and porosity. These properties play vital roles in determining the performance of battery electrodes. In order to improve battery performance it is important to characterize and quantify real electrode microstructures in three dimensions, and understand how these structures affect performance and cycle life.1 X-ray and FIB-SEM techniques have been attracting a lot of interest in the field of batteries and fuel cells due to their ability to characterize electrode structure at the length scales relevant for their operation.2-5 Porous carbon electrodes play an important role in both battery and fuel cell operation, where parameters such as porosity, tortuosity and pore-size distribution determine the transport properties of the electrode, as well as the kinetics of the electrochemical reactions.6 Therefore, a thorough quantitative microstructural characterization of porous-carbon electrodes is a pre-requisite for a complete understanding of the electrode behavior. However, the quantitative 3D microstructural characterization of the porous-carbon electrodes commonly used in battery and fuel cell devices is challenging. One of the biggest difficulties in the 3D imaging of battery materials in the characterization of carbon due to (i) the low X-ray attenuation coefficient when using X-ray imaging and (ii) the non-uniform interaction with the ion beam when using FIB-SEM imaging. Lithium Iron Phosphate (LFP) LiFePO 4 is a commercially available electrode material for Li-ion batteries for electric vehicles and energy storage applications, 7,8 and was used as the basis for this study. This interest is motivated by the many advantages of this material, which include excellent cycle life and a high intrinsic safety.9 It is, however, ...

Modelling of redox flow battery electrode processes at a range of length scales: a review

“…261,262 For example, using phase contrast XCT and high-Z compound epoxy-impregnation techniques for FIBSEM, it is possible to achieve good contrast for carbon materials. 263,264 Another technique being utilized is to study the effects of mechanical compression on carbon-based electrodes. 170 Table 6 summarises the range of materials and compression conditions previously reported in the literature (non XCT-based).…”

Mesoscale Effective Property Simulations Incorporating Conductive Binder

“…This disconnect has resulted in a significant effort to develop mesoscale modeling and simulation capabilities within the battery modeling field. [16][17][18][19] Recent advancements in mesoscale imaging techniques have enabled detailed visualization of complex electrode mesostructures, [20][21][22][23][24][25][26][27][28][29][30][31][32] allowing modeling efforts to progress to real electrode morphologies. 20,27,[33][34][35][36][37][38][39][40][41][42] To bridge the gap between mesoscale and cell-level simulations, efforts have been made to extract electrode-scale properties from mesoscale reconstructions.…”

Morphological and Electrochemical Characterization of Nanostructured Li4Ti5O12Electrodes Using Multiple Imaging Mode Synchrotron X-ray Computed Tomography

“…Four isolated LTO secondary particles obtained using the absorption contrast imaging mode. (a) particle (1), (b) particle (2), (c) particle (3), (d) particle (4). The microstructure data for these particles are listed in Table III.…”

“…The high performance LIB requires high capacity active material and optimized electrode structure [1][2][3] which directly influence the overall cell performance such as rate capability, cycle life, and safety. [4][5][6] For example, using in-situ measurement of lithium transport Harris et al 6 showed the necessity for microstructural information to study lithium plating and dendrite growth in a graphite anode during the battery charging process.…”