When 10:00 AM - 12:00 PM Sep 08, 2014
Where Johnson Rooms B & C, Lurie Engineering Center
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Modeling and Simulation of Nanoparticulate Lithium Iron Phosphate Battery Electrodes

Bernardo Orvananos
Thesis Defense

Katsuyo Thornton , advisor

Elucidating the complex charge/discharge dynamics in nanoparticulate phase-separating electrode materials such as lithium iron phosphate, LiFePO4, is a challenging task because of the small temporal and spatial scale associated with the material and the process. During the charge/discharge cycles of nanoparticulate LiFePO4 electrodes, phase separation inside the particles can be hindered even when a thermodynamic driving force for phase separation exists. In such cases, particles may (de)lithiate via a process referred to as interparticle phase separation, which involves Li redistribution between particles. The role of interparticle Li transport and multi-particle (de)lithiation kinetics could be the key to understand these processes. In this thesis, the complex dynamics of lithium iron phosphate is investigated based on the particle-level electrochemical dynamics (PLED) and the porous electrode theory (PET). PLED combined with a phase field model and the Smoothed Boundary Method is utilized to study the kinetic processes of interparticle phase separation. Using this approach, simple two-particle systems are examined to elucidate the detailed dynamics of the lithiation/delithiation process. Additionally, more realistic structures consisting of many particles are utilized to analyze more complex cases of interparticle phase separation. The dependence of the electrochemical dynamics on (i) the exchange current density, (ii) the particle position, (iii) the presence of intraparticle phase separation, (iv) the particle size distribution, (v) the particle connectivity, and (vi) the surface free energy are elucidated. Simulations based on PET are employed to examine the overall behavior of the cell; these simulations elucidate the position dependence of the electrochemical dynamics on a coin-cell battery experimentally mapped. This thesis presents a comprehensive study on the interactions between LiFePO4 nanoparticles and their effect on battery performance.