Anode Overhang in Commercial Cells

Anode overhang is intentional as cathode overhang can result in:

• potential safety issues
• dendrite growth
• accelerated aging

The issue is that extra anode material increases cost, weight and volume of the cell. Hence it is important to design the cell with the right amount of anode overhang taking into account the manufacturing process variability and quality control inspection capability.

Here we look at data from a number of sources and listed by chemistry:

• Lithium Ion
  • LFP
    • HAIDI HDCF18650 1.8Ah: 8.8%
    • Sinopoly 180Ah: Large-format prismatic with anode overhang of 4.9%
    • Calb 180Ah: Large-format prismatic with anode overhang of 5.7%
  • NCA
    • Tesla Model 3: The overhang accounts for 7.3%
  • NMC
    • Samsung SDI (NMC111): Post-mortem analysis revealed the anode overhang was 9% of the total anode active surface
    • LG INR18650-MJ1 (NMC811): 7% overhang
    • Volkswagen ID.3: The passive area of the negative electrode (overhang) accounts for 2.5%
• Sodium Ion
  • Transition Metal Oxide
    • NA18650–1250 (NFM/Hard Carbon): 8% anode overhang

In commercial lithium-ion and sodium-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%.

This post has been built based on the support of and sponsorship from: Quarto Technical Services, Eatron Technologies and About:Energy

Manufacturing Quality Control

The anode overhang data as a percentage is interesting and helpful for quick estimations of material. However, it is not the right way to express it in terms of cell design.

The Anode Overhang is basically based on how good your Cmk… machine capability is.. and the resulting Cpk you can ensure.

So it’s designed as a dimensional oversize that you at least THINK you can ensure (x ray very helpful but not that great) and the scrap you can tolerate.

So sometimes for a given format, larger cells would have a similar overhang dimensionally, but smaller percentage-wise.

Cylindrical cells sometimes add extra anode wraps in the core for core support, and sometimes even quite a bit of overhang on the OD to get some separation between the anode and cathode ends. This is a bit of a % hit compared to prismatics/pouches.

Looking at the Anode Overhang:

• Lithium Ion
  • LFP
    • HAIDI HDCF18650 1.8Ah Wound Cylindrical: 1.5mm (Cathode = 56mm, Anode = 59mm)
    • Sinopoly 180Ah Stacked Prismatic: 2.5mm (Cathode = 215x154mm, Anode = 220x159mm)
    • Calb 180Ah Stacked Prismatic: 2 to 2.5mm (Cathode = 220x153mm, Anode = 225x157mm)
  • NMC
    • LG INR18650-MJ1 (NMC811) Wound Cylindrical: 0.5mm (Cathode = 59mm, Anode = 60mm)
• Sodium Ion
  • Transition Metal Oxide
    • NA18650–1250 (NFM/Hard Carbon) Wound Cylindrical: 1mm (Cathode = 57mm, Anode = 59mm)

The related subjects now are winding and stack alignment. Please do share any details, data or capability for different approaches.

References

1. Johannes Philipp Fath, Lennart Alsheimer, Mathias Storch, Jochen Stadler, Jochen Bandlow, Severin Hahn, Ralf Riedel, Thomas Wetzel, The influence of the anode overhang effect on the capacity of lithium-ion cells – a 0D-modeling approach, Journal of Energy Storage, Volume 29, 2020
2. 2.5mmMehmet C. Yagci, René Behmann, Viktor Daubert, Jonas A. Braun, Dirk Velten, and Wolfgang G. Bessler, Electrical and Structural Characterization of Large-Format Lithium Iron Phosphate Cells Used in Home-Storage Systems, Energy Technol., 9: 2000911
3. Luiza Streck, Thomas Roth, Hannah Bosch, Cedric Kirst, Mathias Rehm, Peter Keil and Andreas Jossen, Self-Discharge and Calendar Aging Behavior of Li-Ion and Na-Ion Cells, Journal of The Electrochemical Society, Volume 171, Number 8
4. Wätzold, F.; Schlösser, A.; Leistikow, M.; Kowal, J. Design Analysis of 26650 and 18650 LFP Cells for High Power and Low Temperature Use Cases. Batteries 2025

See also

Anode Overhang