Tap density is the powder density and as the name suggests the container is tapped to encourage it to settle. Several parameters influence tap density:
- Particle size: Larger particles are generally more spherical, indirectly contributing to a higher tap density.
- Shape of secondary particles: Smooth, spherical particles tend to pack more efficiently, resulting in higher tap density.
- PSD uniformity: A narrower PSD (smaller D90/D10) improves packing behaviour, again leading to a higher tap density.
How Particle Size Distribution (PSD) Affects Cell Capacity
The PSD of active materials directly impacts their tap density and compactibility—two critical factors that determine how densely an electrode can be packed during calendaring. A higher tap density allows for denser coatings, which is essential when aiming for higher energy density in cells.
Tap density and PSD ultimately feed into how the electrode responds on the calendering line – see Hot versus Cold Roll Calendering and Importance of Electrode Parameter Changes After Calendaring in Lithium-Ion Cell Production for more on that step.
See also: The Importance of Electrode Density