Abstract
The rapid growth of electric mobility has increased the demand for batteries capable of with- standing fast charging without compromising their performance or lifetime. The objective of this Master’s Thesis is the optimization of cathode composition, loading, and mechanical pressure in lithium-ion batteries (LiBs) using NMC811-based cathodes, to enable fast charging.A series of coin half-cell experiments were performed to analyze the effects of varying cathode composition, cathode loading, and cell mechanical pressure on specific capacity, charge transfer resistance, and capacity loss under fast-charging conditions. A systematic experimental design was employed to ensure consistent and comparable results. The experimental procedure involved the fabrication of coin and pouch cells, followed by electrochemical cycling tests and electrochemical impedance spectroscopy (EIS). Structural characterization of the cathode materials was performed using X-ray diffraction (XRD), which provided insights into their structural integrity and degra- dation mechanisms.
The findings reveal that a balanced cathode composition with at least 5 wt% polymer binder and an active material-to-conductive agent ratio of 17 is critical for maintaining fast charging (2C rate) and minimizing degradation. Additionally, cells with lower cathode loading outperformed those with higher loading, and applying mechanical pressure during assembly significantly enhanced electrochemical performance.
Furthermore, the effect of fast charging on the electrochemical performance of pouch full-cells with a graphite anode was studied. Although the pouch full-cells exhibited lower charge transfer resistance and Warburg impedance compared to coin half-cells, they were unable to support fast- charging rates. This limitation is attributed to the intercalation kinetics of lithium ions into the graphite anode, where lithium must diffuse into the bulk material to form LiC6. In contrast, the coin half-cells, which used lithium metal as the counter electrode, allowed lithium ions to accumulate on the surface without requiring intercalation, thus facilitating faster charging despite higher resistance and capacitance.
This work contributes to the development of faster-charging batteries and offers guidance for future studies aimed at improving electrode design for electric vehicle applications.
| Date of Award | 2025 |
|---|---|
| Original language | English |