Optimization of electrode dispersions for advanced lithium-ion batteries

Galantowicz, Joanna (2025). Optimization of electrode dispersions for advanced lithium-ion batteries. University of Birmingham. Eng.D.

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Abstract

Ni-rich cathodes are increasingly vital in energy storage due to their high energy density and reduced cobalt dependence. These materials provide higher capacities, which extend battery life and range. However, Ni-rich cathodes pose significant manufacturing challenges. Their high reactivity in the ambient leads to moisture and carbon dioxide absorption, decreasing performance. Additionally, processing issues like slurry gelling hinder large-scale production. Advanced manufacturing techniques are needed to enhance material stability, processability, and quality, ensuring commercial availability. To address the manufacturing challenges associated with Ni-rich cathode active materials, five multifunctional experimental additives were employed to modify their surfaces. The success of the surface modifications was confirmed using FT-IR, XPS, P-XRD, and electrochemical evaluation, including EIS and cycle life assessments performed for the most promising additive. FT-IR and XPS spectroscopy identified effective surface modification of NMC811. XRD analysis confirmed the rhombohedral R3̅m structure of NMC811 remained unchanged after modification, with no impact on crystallinity or bulk structure stability. Finally, electrochemical evaluation demonstrated improved performance of modified NMC811, with reduced bulk resistance, reduced CEI impedance, enhanced cycle stability, and increased discharge capacities compared to pristine NMC811.
The study also investigated the degradation aspect of lithium-ion battery cathode surfaces due to prolonged air exposure, identifying a delithiation process followed by the formation of residual lithium compounds (RLC). Surface modification of NMC811 with a surfactant additive was found to impact impurity formation, with FTIR and STA results showing reduced impurities at low concentrations. In comparison, higher concentrations led to increased mass loss due to water adsorption. XRD analysis confirmed structural stability. At the same time, the unmodified Pristine NMC811 surface showed significant degradation after 7 and 14 days of exposure, transitioning from the rhombohedral R-3m phase to spinel Fd-3m and rock salt. Furthermore, ageing negatively affected electrochemical performance, with pristine samples exhibiting higher impedance and resistive behaviour. Low additive concentrations (0.1 wt.%) mitigated these effects, maintaining better conductivity and capacitive properties, while higher concentrations increased resistance, as shown by Electrochemical impedance spectroscopy (EIS). Air exposure to the stabilised NMC exacerbated the capacity decline. In conclusion, optimised surfactant concentrations (0.1–0.2 wt.%) improve the stability of Ni-rich cathodes, balancing surface protection and electrochemical properties.
Finally, the influence of surface modification on Ni-rich cathode inks was analysed in NMP-based systems in order to improve ink processability and stability. The study also showed that small amounts of these additives stabilised NMP-based Ni-rich cathode inks by improving dispersibility and surface stability, leading to better microstructural outcomes. Rheological changes were confirmed through SEM/EDX and four-point probe measurements, correlating with improved electrode performance after
calendaring. High-capacity retention, improved rate and cycling stability. In water-based inks, the surface of NMC955 was modified with low surfactant levels. However, gas generation from aluminium current collector corrosion affected electrode quality and electrochemical performance. Dry-coating methods, before the addition of water and water-based binders, offered better stability and performance than wet-coating approaches.
The most successful additive (ER1) suppressed the electrode slurry gelation with enhanced ambient air stability and improved electrochemical performance at low dose levels. The methods and tools utilised could also be relevant for other cathode materials.

Type of Work:

Thesis (Doctorates > Eng.D.)

Award Type:

Doctorates > Eng.D.

Supervisor(s):