Silicon (Si) has emerged as a promising material for Li-ion battery anodes due to its exceptional gravimetric capacity, surpassing conventional graphite.
However, Si’s large volume changes during cycling present challenges. A recent study from the Department of Chemistry – Ångström Laboratory, Uppsala University, explored how Si particle size affects both electrode cycling properties and the processing characteristics during electrode preparation.
Si Particle Size and Electrode Performance
Larger Si particles (micrometer-sized) experience more severe decomposition during cycling compared to smaller particles (nanometer-sized). Combining micrometer-sized Si with graphite seems to be the optimal approach for achieving both high capacity and stability. However, studies have shown successful cycling of electrodes with micrometer-sized Si through innovative approaches.
Processing Characteristics
The morphology and surface chemistries of Si and graphite significantly differ, influencing the choice of binders and solvents for slurry preparation. Water-based systems, favored for their environmental safety, have become standard.
Effect of Si Particle Size on Slurry Rheology
Slurries containing micrometer-sized Si particles behave more like a liquid, while those with nanometer-sized Si exhibit viscoelastic tendencies, even with Si as a minor component. The ideal slurry displays shear-thinning behavior, aiding in both slurry settling prevention and even mass loading. These rheological properties directly influence the quality of electrode coatings.
Si Particle Size and Suspension Behavior
In the absence of binders, nm-Si particles form a stable suspension, showcasing an almost constant and elastic response. In contrast, μm-Si suspensions exhibit lower moduli and instability at low shear rates, suggesting a more liquid-like behavior.
These differences in flow behavior are particularly pronounced at relevant coating speeds.
Key Takeaways:
- Particle size significantly impacts Si electrode performance and processing characteristics.
- Micrometer-sized Si particles offer potential for cost-effective high-capacity anodes, especially when combined with graphite.
- Water-based systems using Na-CMC and SBR are preferred for Si and graphite slurries.
- Surface area concentration of Si particles is crucial for predicting and controlling slurry rheology.
Conclusion
Understanding how Si particle size influences slurry behavior provides valuable insights for optimizing electrode manufacturing processes. Studies like this one lay the groundwork for further advancements in Si-based anodes, bringing us closer to high-capacity, economically viable Li-ion batteries.