Modeling of a non-aqueous Li-O2 battery incorporating synergistic reaction mechanisms, microstructure, and species transport in the porous electrode

Abstract

Li-O2 batteries are considered to be the next generation of new energy storage technology due to the extremely high theoretical energy density. The microstructure of the porous electrode takes an important role in the battery performance since the solid discharge product Li2O2 occupies the surface and void volume, increasing the transfer resistance. The product morphology and reaction mechanisms are affected by the electrode catalytic activity, electrolyte, and operating conditions. To systematically portray the microscopic processes in non-aqueous Li-O2 batteries, a model by coupling the above multiple factors is developed in this work. Unlike previous models where a single surface pathway or pore size distribution is considered alone, the present model focus on the interdependence of the reaction mechanisms and the electrode microstructure evolution, in which the reaction pathways are controlled by dynamic pore size. Moreover, the effective species transport relationship is modified, and the volume fraction and the corresponding active area of the products with different morphologies are calculated. The simulation results demonstrate the significant effects of microstructure on performance and explain the phenomenon of two discharge platforms, which comes from the tortuous variation of the electrode active area and are further influenced by current density and oxygen diffusion coefficient. This work is expected to guide the design of electrode structures and operating conditions for achieving improved performance.