Geometric Optimization of Li-O2 Battery Cathodes with Pore Structure By Meso-Scale Modeling and Simulation Pursuing Practical Systems
Couples of numerical models to assist in predicting the performance of the cell have also been developed by modifying the models developed for Li-ion batteries. However, detailed geometrical optimization of cathode components composed of an electrolyte, carbon particles and pores has not been reported. Among the Li-O2battery research community, it has been the norm that reporting specific capacity versus only carbon weight but for practical and precise assessment, all the components comprising cathode including electrolytes should be considered as they also add mass to total cathode weight. Consequently, the optimization of the ratio of the components is absolutely necessary for practical system design.
Here, we modeled and simulated the Li-O2 cell with an electrolyte and with an electrolyte and pores. Percolation limit for electric conduction was introduced to define minimum volume occupied by carbon particles. Dynamic electrodeposition of reaction products with the surface passivation effect that expresses exponentially increasing electric resistance as the film growing was introduced by using the Comsol multi-physics electrodeposition module. Random distribution of conductive particles was realized by using the Bruggeman equation for charge transport thorough a media. The simulated results were verified by experimental results. Li-O2 cells with the cathode comprising of Printex carbon as the conductive media and PEO (polyethylene oxide) containing LiTFSI (lithium bis(trifluoromethanesulfonyl) imide) as the electrolyte were fabricated with various compositions and their charge discharge properties were characterized. Results from both simulation and experiments showed good agreement in trends for flooded type cells and suggests optimized the ratio of components.
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