Virtual Design of next-generation zinc-air batteries
Clark, Joseph Simon
Institut für Theoretische Chemie
LicenseCC BY-SA 4.0 International
In the on-going search for post-lithium-ion battery technologies, metal-air batteries stand out as promising candidates with high energy density. Zinc-air batteries (ZABs) in particular are the most advanced metal-air chemistry, and are based on cheap, abundant, and safe materials. With a theoretical energy density over 6000 Wh/L, ZABs could play a pivotal role in grid-scale renewable energy storage and electric mobility applications. Unfortunately, both the electrical rechargeability and calendar lifetime of ZABs are limited. New electrolyte materials are needed to overcome these challenges. The application of physics-based numerical modelling and simulation can accelerate the development of ZAB materials and cell architectures. Over the course of this work, I derive a new quasi-particle framework for continuum modelling of aqueous electrolytes. This method significantly improves the computational effort required to simulate electrolyte transport in aqueous ZABs and opens new complex electrolytes to model-based investigation. Thermodynamic speciation models and 1D continuum models are applied to evaluate the performance of ZABs with a range of electrolyte compositions. These models allow the equilibrium composition of aqueous electrolytes and the solubility of various precipitates to be determined. I then simulate the dynamic and spatially resolved 1D concentration and multi-phase volume fraction profiles that develop in a ZAB cell during operation. This method can be applied to better understand the performance of current alkaline and near-neutral ZABs and envision next-generation designs. Industry-standard primary ZABs currently contain aqueous alkaline KOH electrolytes. These batteries have good discharge characteristics, but the Zn electrode changes shape when cycled and the electrolyte slowly degrades as it absorbs CO2 from air. The lifetime of these cells is limited to just a few months. Aqueous near-neutral electrolytes have been proposed to address these challenges. ZABs with pH-adjusted NH4Cl-ZnCl2 (LeClanche electrolyte) have shown good cyclability and are not subject to carbonation. But the strongly oxidizing nature of chlorine and the precipitation of unwanted solids hinders the development of a robust and high energy density battery. In spite of these challenges, aqueous near-neutral ZABs are beginning to be commercialized for some large-scale stationary applications. In this dissertation I present a theory-based method for evaluating the performance of current systems and designing new aqueous electrolytes for next-generation ZABs. Beginning with fundamental thermodynamics and moving up to cell-level engineering, I identify the important characteristics required for new electrolyte materials and highlight an example of electrolyte design in action. By applying a rational design method, I show the promising potential for long-life rechargeable ZABs based on abundant and non-toxic materials and indicate topics for future research.
Subject HeadingsElektrochemie [GND]
Computational chemistry [GND]
Next generation energy [LCSH]