Multi-Methodology Modeling and Design of Lithium-Air Cells with Aqueous Electrolyte

Metal-air batteries are being investigated as alternative to state-of-the-art lithium-ion batteries for mobile and stationary applications due to their higher specific energy and potentially lower cost. Modeling and simulation techniques allow a better understanding and improvement of the complex mechanisms and properties of metal-air batteries.  Here we present combined modeling and experimental results on a lithium-air (Li/O₂) battery with aqueous alkaline (LiOH) electrolyte using three different modeling methodologies, (i) Lattice-Boltzmann simulations on the porous electrode scale, (ii) multi-physics continuum modeling on the single-cell scale and (iii) system simulation of a Li/O₂-operated electric vehicle.

Lattice-Boltzmann simulations on experimentally reconstructed Ag-based gas diffusion electrodes (GDE) are performed in order to derive multi-phase transport parameters, in particular, saturation/pressure relationships and effective diffusion coefficients. The computational domain of the 1D continuum model consists of the gas-diffusion electrode as cathode, a porous separator, and a lithium metal anode. The model includes a detailed description of the multi-step electrochemistry including dissolution of O₂into the liquid electrolyte, oxygen reduction to hydroxyl ions, and nucleation and growth of the solid reaction product LiOH [1]. The model is validated with experimental half-cell measurements over a wide range of conditions. The multi-physics model is integrated into a system simulation of a battery electric vehicle, including electric engine and regenerative braking. The model is used to simulate driving cycles (Fig. 1), which allow to quantify practical energy and power densities and to investigate the potential of lithium-air technology as next-generation battery for electromobility.

As key result, the alkaline lithium-air battery offers the interesting capability of high-power cycling using only liquid-phase dissolved intermediates (O₂ + 4e^– + 2 H₂O ⇄ 4 OH^–) coupled to high-energy content due to solid product formation (Li⁺ + OH^– + H₂O ⇄ LiOH·H₂O). This dual functionality can be exploited for the driving cycle using model-based cell design.

[1]     B. Horstmann, T. Danner, and W. G. Bessler, “Precipitation in aqueous lithium-oxygen batteries: a model-based analysis,” Energy & Environmental Science 6, 1299–1314 (2013).