Anode Overhang - Battery Design

Anode Overhang is the extra material in a battery cell’s anode that extends past the intended boundaries.

This is intentional as cathode overhang can result in:

dendrite growth
accelerated aging
potential safety issues

Hence a measure of this is important in any cell assembly system.

For examples of measured overhang values on real commercial cells, see Anode Overhang in Commercial Cells.

It is shown [3] that the evolution of the cell capacity can be described dependent on the size of the anode overhang and the storage SOC using a 0D-modeling approach.

Two Components of Overhang

(A) The anode excess on the anode facing the cathode: Basically, the extra surface from the anode relative to the cathode, minus the …

(B) … the anode excess on the anode side facing nothing: typically one full side of anode from the external anode layers in a stack, for example, but you can also find it in a wound configuration at the beginning and the end of the jelly roll, as you mention in your updated article.

Why bothering with these considerations?

There is a lot of anode overhang variability from one cell to another. The purpose of considering both A and B is to explain this discrepancy, mainly by linking it to the battery capacity and form factor. Therefore, you could really highlight differences between manufacturers’ process control (at least on stacking/winding), also assessing if whether or not there is a correlation with the chemistry, the application, the charge time, the durability

For example, wound cells may have lower A than stack cells, but higher B, potentially highlighting an easier alignment with winding compared to stacking. Comparing just A + B may miss this consideration, especially considering that B depends also on the number of layers (cells with higher layer count, typically for power oriented applications, have a lower B for a given cell format). Also, the bigger the cell, the lower B.

For stack cells, similarly to the wound cells, the discrepancy may come from the number of sheets per substack. Higher sheet count leads to lower B, while A may remain the same regardless of the sheet count. Considering only A + B misses this assessment.

With a big and precise enough database, there are some nice insights to extract (Michel Ulldemolins).

Commercial Cells

In commercial lithium-ion cells, the geometric anode overhang typically falls between 2% and 10%. However, the total coated area of the anode can exceed that of the cathode by as much as ~12%.