Elongation
High, uniform elongation in rolling, transverse and 45° directions lets the foil follow the punch into the pocket corners. Laminators test this as a minimum elongation and by forming trial pockets to a target depth.
Battery materials guide
8021 Aluminium Foil for Lithium Pouch Cell Packaging
8021 aluminium foil is the barrier layer inside the aluminium-plastic laminated film that encloses lithium-ion pouch cells. Supplied in soft O temper, typically 25 – 60 µm thick, it keeps moisture and oxygen out of the cell while stretching enough to be cold-formed into deep cell pockets without cracking. This guide explains why 8021 is used, how the laminate is built, which properties matter and how to specify the foil.
- Alloy
- 8021 (Al-Fe, ≈ 1.2 – 1.7 % Fe)
- Temper
- O (fully annealed)
- Thickness
- 0.025 – 0.06 mm
- Width
- 100 – 1650 mm
The role of aluminium foil in a pouch cell
A pouch cell has no rigid can. Its electrodes and electrolyte are sealed inside a flexible laminate, so that laminate alone must keep water vapour out for the life of the battery. Even a few hundred parts per million of water reacts with the LiPF6 salt in the electrolyte to form hydrofluoric acid, which degrades the cell. Polymer films cannot provide that barrier; a continuous aluminium foil can.
The foil also has to survive the way pouches are made. Cell makers cold-form, or deep-draw, a pocket into the flat laminate to hold the electrode stack. Pocket depths of several millimetres stretch the foil hard, especially at the corners. If the foil necks or cracks there, the barrier is lost and the cell fails, often only after months in service.
8021 meets both needs. It contains about 1.2 – 1.7 % iron and very little silicon, which produces many fine Al-Fe intermetallic particles. After full annealing these particles pin a very fine, uniform grain structure, giving high elongation and isotropic deformation: the foil stretches evenly in all directions instead of thinning locally. That is why 8021 and its close relative 8079 dominate battery pouch and cold-form pharmaceutical foil.
8021 battery pouch foil specification
Typical supply range
- Alloy / temper
- 8021-O (EN AW-8021, JIS A8021)
- Thickness
- 0.025 – 0.06 mm; 35 µm and 40 µm are the most common gauges
- Width
- 100 – 1650 mm, slit to the laminating line
- Surface
- Both sides bright or one side matt; fully degreased, wettable for conversion coating and adhesive
- Core
- Aluminium or steel core, 76 mm or 152 mm ID
- Main use
- Aluminium-plastic laminated film for lithium-ion pouch cells
| Element | Limit (wt %) | Note |
|---|---|---|
| Iron (Fe) | 1.2 – 1.7 | Main alloying element; forms fine particles that refine grain |
| Silicon (Si) | ≤ 0.15 | Kept low to avoid coarse Al-Fe-Si phases |
| Copper (Cu) | ≤ 0.05 | Impurity |
| Others each / total | ≤ 0.05 / 0.15 | |
| Aluminium (Al) | Remainder | About 98 % |
Composition per the registered 8021 limits (Aluminum Association / EN 573-3). Mechanical requirements for battery foil are normally set by the laminate maker's own specification, typically a minimum elongation and a cupping or forming-depth test, rather than by a general foil standard.
How a pouch cell laminate is built
| Layer (outside → inside) | Typical material and gauge | Function |
|---|---|---|
| Outer layer | Oriented nylon (ONy, polyamide), about 15 – 25 µm; sometimes PET or PET/nylon | Puncture and abrasion resistance, supports the foil during forming |
| Adhesive | Polyurethane dry-lamination adhesive | Bonds nylon to foil |
| Barrier layer | 8021-O or 8079-O foil, about 35 – 40 µm | Moisture and gas barrier |
| Surface treatment | Chemical conversion coating on the inner face | Resists attack by electrolyte and HF, keeps the inner layer bonded |
| Tie layer | Acid-modified polypropylene or adhesive | Bonds the sealant to the foil |
| Sealant layer | CPP (cast polypropylene), about 30 – 80 µm | Heat sealing and electrolyte resistance |
Finished laminates are usually sold by total thickness: around 88 µm for thin consumer cells, about 113 µm as a common general grade (for example 25 µm nylon, 40 µm foil and 40 µm polypropylene plus adhesives), and about 150 µm or more for large EV and energy-storage cells that need deeper pockets and more puncture resistance. The foil gauge rises with pocket depth: a thicker foil spreads strain over more metal and resists cracking.
Properties that decide forming depth and reliability
Grain size
A fine, even grain (helped by 8021's iron particles and controlled final annealing) prevents orange-peel and local necking during deep forming.
Pinholes
At 35 – 40 µm, good battery foil is essentially pinhole-free. Pinholes come from inclusions and rolling defects, so melt cleanliness and filtration matter.
Surface cleanliness
Residual rolling oil weakens the conversion coating and adhesive bond. Battery foil is annealed to burn off oil and checked by wettability (brush or dyne) tests.
Gauge and flatness
Thickness variation across the width causes uneven lamination and inconsistent forming. Tight tolerance and good shape keep the laminating line stable.
Mechanical strength
Tensile strength in O temper is modest; what matters is the combination with nylon, which carries much of the load during forming.
8021 compared with 8079, 8011 and cathode foil
| Foil | Main alloying | Typical temper and gauge | Main battery-related use |
|---|---|---|---|
| 8021 | Fe 1.2 – 1.7 % | O, 25 – 60 µm | Pouch cell laminate barrier; cold-form blister foil |
| 8079 | Fe 0.7 – 1.3 %, Si 0.05 – 0.30 % | O, 25 – 60 µm | Pouch laminate barrier (alternative to 8021); flexible packaging |
| 8011 | Fe 0.6 – 1.0 %, Si 0.5 – 0.9 % | O or hard tempers, 6 – 200 µm | Packaging foil; some current-collector grades in H18 |
| 1060 / 1070 / 1235 | ≥ 99.35 – 99.7 % Al | H18, 10 – 20 µm | Cathode current collector foil |
8021 generally gives the highest and most uniform elongation of the group, which is why it is preferred for the deepest pockets. 8079 is used where its forming is sufficient and supply or cost favours it. Pouch laminate foil and cathode current-collector foil are completely different products: the collector is a thin, hard, high-purity foil coated with cathode material inside the cell, whereas 8021 is a soft barrier layer outside it. See our current collector foil guide for that product.
Supply and documentation
Metline supplies 8021-O foil to laminate converters and battery material buyers worldwide, slit to width and packed for clean-room handling. Each lot ships with a mill test certificate (EN 10204 3.1) reporting chemistry and mechanical results; we can add surface and dimensional inspection reports and arrange third-party testing when a programme requires it.
How to specify 8021 pouch foil
- Define the laminateTotal laminate thickness, foil gauge and the deepest pocket you plan to form.
- Set foil propertiesMinimum elongation (and directions), tensile range, pinhole limit and wettability.
- Give dimensionsWidth and tolerance, core ID, maximum coil OD or weight, splice rules.
- Agree surfaceBright or matt faces, oil residue limit, and whether conversion coating is applied by you or upstream.
- Confirm documents and packingCertificates, inspection reports, and moisture-proof, dust-free packing with desiccant on export pallets or in cases.
Beyond batteries, the same 8021-O foil is used for cold-form (Alu-Alu) pharmaceutical blisters and other high-barrier laminates where deep drawing is needed.
References and standards
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
- EN 573-3 – Chemical composition and form of wrought products
- EN 546-2 – Aluminium and aluminium alloys: foil, mechanical properties
- JIS H4160 – Aluminium and aluminium alloy foils
8021 pouch cell foil: frequently asked questions
What is the difference between 8021 and 8011 aluminium foil?
8021 has more iron (1.2 – 1.7 %) and very little silicon, giving a finer grain and higher, more uniform elongation in O temper. That suits deep cold-forming in pouch laminates and Alu-Alu blisters. 8011 contains both iron and silicon and is the general packaging foil.
What is the difference between 8021 and 8079 foil?
Both are soft Al-Fe foils used as barrier layers. 8021 has higher iron and usually forms deeper pockets; 8079 has a little less iron, some silicon and is widely used in flexible packaging and some pouch laminates.
Is 8021 aluminum foil used as cathode foil?
No. Cathode current collectors use thin, hard, high-purity foil such as 1060, 1070 or 1235-H18. 8021-O is the soft barrier layer in the outer pouch laminate.
What thickness of 8021 foil is used in pouch cells?
Most laminates use 35 or 40 µm foil. Thinner gauges suit small consumer cells; thicker foil, up to about 60 µm, is used for large cells with deep pockets.
Why must the foil surface be treated?
Electrolyte that reaches the inner face can form hydrofluoric acid, which attacks untreated aluminium and causes the sealant to delaminate. A conversion coating on the inner face protects the metal and keeps the bond.
Can Metline provide test documents?
Yes. Each lot comes with an EN 10204 3.1 mill certificate showing chemistry and mechanical properties, and inspection or third-party test reports can be added on request.
Sourcing 8021 foil for pouch laminate?
Send the gauge, width and forming requirements. Our team will reply with a specification and delivered price.
