Advanced optimization procedures for lithium-ion battery insertion cathodes

This work presents a comprehensive investigation into optimizing cathode formulations for lithium-ion batteries (LIBs), focusing on advancing energy density, C-rate capability, and cost efficiency. A special focus was on the measurement and assessment of the electronic conductivity of cathodes. Electrode slurries with varying formulations were prepared and coated, examining the effects of cathode active materials (CAMs), binders, and conductive additives (CAs). Variations in electrode loading and density were done to provide a holistic perspective on electrode production parameters. Electrochemical performance was evaluated through half-coin cells (HCC), electronic resistance measurement (ERM), and electrochemical impedance spectroscopy (EIS) using three-electrode cells. Experimental data were used to develop semi-empirical models and behavioral schemes, offering new insights into cathode design. The first key outcome highlights a holistic understanding of cathode development. Comparisons of CAMs such as Lithium-Nickel-Cobalt-Manganese oxide (NCM) and Lithium-Manganese-Iron phosphate (LMFP) emphasized the impact of crystal density, press density and specific capacity on the reachable volumetric energy density. Electrode design parameters like electrode loading, press density and porosity were assessed for their impact on C-rate capability, cost and volumetric energy density. Temperature and state-of-charge (SoC) effects on resistance types were characterized, revealing essential impacts on electrode kinetics. Secondly, the thesis focuses on characterizing electronic resistance at the electrode compound and electrode/current collector interface and its correlation with typically used performance indicators such as half coin cells. Using a newly commercially available electronic resistance measurement device (HIOKI RM2610), electronic resistances were measured, and important impact factors were identified. A total electronic resistance (TER) threshold of 0.25 Ω∙cm² was established, below which further performance gains were not measurable in half coin cells. These findings can enable predictions of cathode performance based on electronic resistance measurement (ERM) results, a major contribution to the field of cathode development. Lastly, the gained insights were applied to develop a more efficient cathode optimization strategy. The integration of electronic resistance measurement (ERM) can significantly reduce the need for extensive electrochemical testing and can therefore help to make electrode development more time and cost efficient.