Modeling of Transport Processes in Aqueous Li-O Cathodes

Kurzfassung

Metallic Lithium-Oxygen (Li-O) batteries with a very high theoretical energy density (11.680 Wh/kg) are a very promising alternative to conventional combustion technologies in the mobility sector. In this talk we will present results from our multi-phase modeling framework for lithium batteries and fuel cells. The framework is capable of describing the formation and transport of multiple gaseous, liquid and solid phases in aqueous and aprotic Li-O batteries. Major problems in Li-O systems arise from the formation of solid products within the porous structure of the oxygen electrode. In our model of an aqueous Li-O battery we take into account the formation of solid LiOH•H2O in the porous electrode and separator. LiOH•H2O clogs the pore space and limits the transport of reactants, to the active surface sites. The performance of the system can be greatly improved by Gas Diffusion Electrodes (GDE). As previous research on Alkaline Fuel Cells (AFC) provides a good basis for modelling of GDE in alkaline media, it is somehow surprising that only non-aqueous systems are tackled in the modeling literature so far. Simulation results for our detailed modeling approach of the GDE-Cathode in aqueous lithium hydroxide solution are presented. We model capillary-pressure driven transport of the liquid electrolyte in the GDE and discuss the dynamic equilibrium between the liquid electrolyte and gaseous oxygen. Capacity limitations due to the formation of a LiOH•H2O film at the anode surface are predicted by the simulations. Model parameters are calibrated and validated against experimental data of half-cell experiments at model GDEs in an aqueous one molal LiOH solution, which were also conducted at our institute.