Three Dimensional Reconstruction of Solid Oxide Fuel Cell Electrodes Using Focused Ion Beam - Scanning Electron Microscopy

2019 ◽  
Vol 7 (1) ◽  
pp. 1879-1887 ◽  
Author(s):  
James Wilson ◽  
Worawarit Kobsiriphat ◽  
Roberto Mendoza ◽  
Hsun-Yi Chen ◽  
Tom Hines ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Three Dimensional ◽  
Solid Oxide ◽  
Oxide Fuel ◽  
Fuel Cell Electrodes ◽  
Dimensional Reconstruction ◽  
Scanning Electron

Coupled Mechanical and Electrochemical Analyses of Three-Dimensional Reconstructed LiFePO4 by Focused Ion Beam/Scanning Electron Microscopy in Lithium-Ion Batteries

2018 ◽  
Vol 16 (1) ◽  
Author(s):  
Sangwook Kim ◽  
Hongjiang Chen ◽  
Hsiao-Ying Shadow Huang
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Lithium Ion Batteries ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Three Dimensional ◽  
Lithium Ion ◽  
Electrochemical Degradation ◽  
Total Polarization ◽  
Scanning Electron

Limited lifetime and performance degradation in lithium ion batteries in electrical vehicles and power tools is still a challenging obstacle which results from various interrelated processes, especially under specific conditions such as higher discharging rates (C-rates) and longer cycles. To elucidate these problems, it is very important to analyze electrochemical degradation from a mechanical stress point of view. Specifically, the goal of this study is to investigate diffusion-induced stresses and electrochemical degradation in three-dimensional (3D) reconstructed LiFePO4. We generate a reconstructed microstructure by using a stack of focused ion beam-scanning electron microscopy (FIB/SEM) images combined with an electrolyte domain. Our previous two-dimensional (2D) finite element model is further improved to a 3D multiphysics one, which incorporates both electrochemical and mechanical analyses. From our electrochemistry model, we observe 95.6% and 88.3% capacity fade at 1.2 C and 2 C, respectively. To investigate this electrochemical degradation, we present concentration distributions and von Mises stress distributions across the cathode with respect to the depth of discharge (DoD). Moreover, electrochemical degradation factors such as total polarization and over-potential are also investigated under different C-rates. Further, higher total polarization is observed at the end of discharging, as well as at the early stage of discharging. It is also confirmed that lithium intercalation at the electrode-electrolyte interface causes higher over-potential at specific DoDs. At the region near the separator, a higher concentration gradient and over-potential are observed. We note that higher over-potential occurs on the surface of electrode, and the resulting concentration gradient and mechanical stresses are observed in the same regions. Furthermore, mechanical stress variations under different C-rates are quantified during the discharging process. With these coupled mechanical and electrochemical analyses, the results of this study may be helpful for detecting particle crack initiation.

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